More Musings of an Energy Nerd
So-called radiant floors have an excellent reputation. Many customers report that this type of heating system is comfortable and quiet. Moreover, some suppliers of radiant floor materials and equipment claim that these systems can save energy.
In spite of the purported benefits of this type of heating system, few green homes include a radiant floor heating system. This article will explore why.
What shall we call these systems?
We’ve all seen ads for this type of heating system, including photos showing a barefoot mom watching her baby crawl across the floor. Using photos like this as a guide, is it possible to describe the heat transfer mechanisms in such rooms?
The mother’s bare feet are being heated by conduction. The air near the floor is also being heated; as the warm air rises to the ceiling, it creates a convective loop. So the room is being heated by convection. And, if the floor is warm enough, the mother’s bare arms are being heated by radiation.
In other words, all three heat transfer mechanisms are at work. So why is this a “radiant floor”? The phrase “radiant floor” is misleading, and should be abandoned. It’s more accurate to say that this floor has “in-floor hydronic tubing.”
Three ways to warm up your flooring
There are three types of heated floors:
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130 Comments
Passive Solar and Underslab Insulation
Excellent article. We are building a 1600 sq. ft. passive solar home with slab-on-grade and were originally considering radiant heat until we came across Alex Wilson's article.
One question I have not seen consistently answered, though, is how a passive solar floor should be insulated to optimize the thermal mass while still providing some warmth to the feet during times when the sun is not out or in areas where the sun might not reach. I have seen multiple suggestions, of course, ranging from outside the slab (including shallow frost-protected versions) up to insulation under the entire slab.
We're in a mixed climate (Missouri) and the suggestion from Building Science seem to indicate semi-permeable insulation under the entire slab with no vapor barrier, however I don't know if passive solar factors in to that suggestion.
Any advice for us? Thanks in advance.
Response to Jeff Carroll
Jeff,
In all but the warmest climates, it makes sense to install a horizontal layer of rigid foam directly under your slab -- whether or not your slab is a component of a passive solar design strategy.
The usual layers for a slab on grade, from the bottom up, are: 4 or more inches of crushed stone, a horizontal layer of rigid foam, 6-mil polyethylene, and concrete. You will also need vertical rigid foam at the perimeter of the slab.
There is no advantage whatsoever to choosing vapor-permeable foam at this location. On the contrary: a vapor barrier (the 6-mil poly) is an essential component of this assembly.
You can use an energy modeling program to determine the optimal R-value of your sub-slab foam. Remember: you only get one chance to install sub-slab insulation. No one has ever regretted installing too much insulation in this location, but many builders and homeowners have regretting installing too little insulation.
Adirondack Area; Radiant tubes are a nice addition to a basement
Adirondack radiant tubes in basement floors when basements are used as living space: I can tell you first hand this option is well liked, loved. Another benefit, no baseboard radiators mucking up the walls.
Radiant floors where there is no solar gain, and bathrooms... good place for radiant. And yes I agree that a net zero or PGH homes will not need radiant floor heat covering entire floors, still might work to hit the bathrooms on a timer or not if truly looking to spend zip on energy.
I do look forward though to using mini splits someday soon on a project. I have had a customer install the first mini, but the home is not quite finished and moved into.
So, do "radiant" heat floors emit mostly radiant heat?
As usual, a nicely written synopsis on a popular topic, Martin. I have a question for you, though. As you pointed out, "radiant heat floor", in its typical installation fashion, should more appropriately be called "hydronic in-floor heating", but it begs the question: is most of the heat delivered really radiant?
While it's the conduction property that appeals to so many (like auto shop workers lying on the slab to loosen the rusty exhaust nuts), there are some who feel the real benefit is radiation, however, that same nice sense of warmth a campfire provides on a chilly night. Will a hydronic in-floor system still yield this desired trait at the lower delta-T that super-insulated homes require?
What are the relative components of conduction, convection and radiation in this system? And how much do they contribute to occupant comfort (as opposed to merely warming the room)? As AJ Builder points out, people love 'em in their basements!
Response to Kent Jeffery
Kent,
Q. "What are the relative components of conduction, convection and radiation in this system?"
A. There is no single answer to this question. The answer will vary depending on the amount of clothing worn by any people in the room (radiation is more of a factor for nude people than clothed people); whether they are standing or curled up on a sofa; the thermostat setting; and the temperature of the flooring.
In many well insulated homes, radiation from a hydronically heated floor to bare skin will be a very minor factor. Classic examples of radiant heating require very hot sources of heat: the sun, a blazing wood stove, or a campfire. When the heat source is at 75 degrees F or 80 degrees F, you aren't likely to extend your bare hands and aim them at the floor to warm them up, the way you would when you approach a wood stove.
Aha, good info, BUT...
One must have to live or lived in a radiant-heated house to “get it”, as is not about the price, it's all about the joy of walking barefoot and feeling warm toes. For the same reason some folks buy a Lamborghini or a new $500 golf driver and shoot 100. JP Morgan said once, referring to the price of a boat, “You have no right to own a yacht if you ask that question.’”
Having said that, I found the best way to install a hydronic radiant heating system is to install a good amount of rigid foam under the entire slab, barometric thermostat, run a water line to the air handler coil to provide quick recovery and install supply-only or balanced make-up air. It goes without saying, it all works best with a tight envelope with micro heating and cooling loads.
“Radiant Heat”
I regard the term “radiant heat” to mean a heat distribution system in which radiation plays the most prominent role in the heat delivery. It has to involve a judgment call as implied in the relative term “prominent” because all three forms of heat transfer operate in any type of heat distribution system. So, generally, I would classify a heated floor as a radiant heat delivery means. A heated floor also readily conducts, but only to the extent that there are objects or people to conduct to. Although it also conducts to air and makes convection, but the geometry for that is relatively awkward.
However, aside from the controversy of calling a heated floor a “radiant floor,” I sense that the term “radiant heat” has popularly come to mean a heated floor EXCLUSIVELY. That, I think is an error in terminology. “Radiant heat” could also come from walls or ceiling.
The cast iron “radiator” or “baseboard radiation” do both radiate, but perhaps convection is equally a part of their means of heat distribution. Baseboard radiation in particular is small in terms of a radiant emitter, but as a source of convection, it effectively heats large areas of walls, and thus converts the walls into effective radiant emitters.
I believe the popularity of heated floors comes from the experience of the sense of warmth conducting to peoples’ feet most often in a building envelop that has poor-to-average levels of insulation. This sensory experience is indeed like the experience of standing by a hot campfire on a chilly night. This sensory delight is what sells people on the so-called radiant floor.
On the other hand, if a heated floor were operating efficiently in a superinsulated house, the average person might not even realize that there was a heated floor involved.
Facts please... will the floor feel warm and cozy?
Because I have been roundly and correctly questioned regarding my initial HVAC design (thankfully, before any significant investment made), I've been exploring in detail this question. Opinions are great, but like the sign above my desk says, "Everyone is entitled to their own opinion, but not their own facts". I needed some facts.
Let's say my house is ultra-tight, and super-insulated. And let's say that the design heat load it 10 BtuH per sq. ft. Maybe that's not so "ultra" or "super", but for this discussion, it suffices as I move forward in making my point. Now, 10 BtuH/sf is the design condition, only rarely met. Most of the time the heat flux from my hydronic floor will be much less.
What if I wanted an air temp of 72F, for there I felt “comfortable”? What, then, will be the required temperature of my slab to maintain this design point? Let's say it's REALLY cold outside, and I am near my design load condition of 10 BtuH/sf. If we use Mr. Wilson's heat transfer coefficient of 2 BtuH/sf/deg F for slab to room, which I believe is for combined radiant and convective load transfer, then the Δ-T works out to be = 10 BtuH/sf ÷ 2 BtuH/sf/deg F, or 5 deg F. Add this to my target air temp and the slab temperature targeted will be 77 deg F.
How would this feel on my bare feet? Would I be happy? Well, according to Dr. Bjarne Olesen in his 1977 paper entitled, “Thermal Comfort Requirements For Floors Occupied By People With Bare Feet”, 15% of people will be unhappy at 10 minutes if the slab temperature is less than 79 deg F. On other words, the heat flux needed to keep most people happy standing barefoot on concrete, in a 72 degree room, is 14 BtuH/sf or better (= Δ-T x 2 BtuH/sf/deg F).
According to Dr. Olesen, and incorporated into ASHRAE recommendations, the optimal temperature for comfort standing on a concrete floor is between 79F and 83F (http://www.healthyheating.com/Radiant_Design_Guide/floor-temp-vs-surface-flux-comfort-rev1.png)
FACT – an ultra-tight and super-insulated home requiring heat flux of less than 14 BtuH/sq. ft., heated via hydronic in-floor radiant heat, will leave most people dissatisfied.
Response to Kent Jeffery
Kent,
Q. "Will the floor feel warm and cozy?"
A. The leakier the house, and the thinner the insulation, the cozier the floor will feel.
On the other hand, the tighter the house, and the thicker the insulation, the less likely that the floor will feel warm and cozy.
For most homeowners, installing enough insulation under the floor will do enough good to make the home feel comfortable. Truly uncomfortable homes are usually drafty or have a high degree of thermal stratification between the air near the floor and the air near the ceiling. Building a tight, well insulated envelope gets you where you want to be from a comfort standpoint.
Fact is, the answer is "no"...
... if they expected warm tootsies, that is.
The threshhold for warm foot comfortworks out to 14 BtuH/sq. ft.
Yup, Martin, I've seen the writing on the wall. I really, really thought I wanted a hydronic in-floor heating system, but am fairly certain that it will not meet my expectations, having gone through the exercise in my prior post. Thus, it has been abandoned.
Next sacred cow to be slaughtered? HVAC system that I used to feel I really,really wanted?
Geothermal ground source heat pump.
Response to Kent Jeffery
Kent,
So, it's time to 'fess up: how high was your contractor's bid?
Some people get a $20,000 bid for a ground-source heat pump system. Other bids are closer to $40,000. Where did your contractor's dart land?
Err... um.... well....
I solicited two bids.
First is for 3 zone forced air geothermal with nat'l gas back-up, duct work, desuperheater for DHW, loop field and HRV. That bid is $39,000.
Second is incremental bid, adding hydronic heat throughout most of the house, but retaining forced air in the great room (hydronics w/ hardwood floor debate, anyone?) and second floor. That bid came in at $61,000.
Now, you can see why I am more than happy to have the debate about the relative merit of hydronic in-floor heating settled!
Please, follow me and let's explore this further
I don't want to hijack this excellent post discussion for personal use, so if any readers are interested in following this line of discussion, please follow me over to my other post directly concerning the GSHP question: https://www.greenbuildingadvisor.com/community/forum/mechanicals/33963/why-must-hvac-decisions-be-so-complex-or-geothermal-worth-it
It's engineered to amaze!
Reality or Placebo? Who cares!
I know that walking on a tight house (1ACH50), 2x6 wall with R21 cellulose, 1" rigid foam outsulation, with 2" rigid foam under the slab in CZ4, can give you warm toes and comfortable temps, and so dozens of my clients. At some point, personal experience trumps ΔTs, π, √, or Xⁿ... Do I care if its reality or placebo? NO!
Armando,
Perhaps oddly, every client I have had who wanted in floor heating had never experienced it. They just liked the idea.
In my experience,
When it comes to Geothermal systems, I’ve done many cost estimates and TRUE energy analysis on high-performing, well insulated, super-sealed houses over the last 20 years to know that no Geothermal system can return the investment on houses from 1K to 8K square feet where the heating and cooling loads are typically 1/3-1/4 of a code house. All these houses are in CZ2-CZ5.
Thanks
Thanks Martin. My thoughts exactly on getting the foundation right, so very glad to have your advice on this. Have a good one.
Armando
Yeah, I know where you're coming from. I have in-floor hydronic heating in my garage/shop that I erected last year. Heated with Triangle Tube natural gas condensing boiler. AND I LOVE IT. But, it is built with 2x6 walls, with 2" XPS on the exterior, no spray foam (but I caulked the piss out of it), and has 3 large overhead doors. My energy use this past winter was just over 300 therms, or 30 million Btu's. The boiler ran for 734 hours, so delivered roughly 40,800 BtuH. The sguare footage of my garage/shop is 1800 ft^2, so heat flux works out to 22.7 BtuH/sf. Am I surprised that I love it? No, because the flux exceeds the 14 BtuH/sf threshold I calculated above. I worry, however, that when I finish the insulation, add my vapor barrier, and drywall the place, I might now hardly ever see the boiler fire up, and I might find it cold lying on the floor changing oil.
sub-slab insulation
A few years ago we worked on the home of a high-level researcher for a major environmental organization. The home was (and is) heated with an oil-fired boiler. Before we had been hired, the owners had built a slab-on-grade family room addition with hydronic tubing embedded in the slab, in no small part because the contractor had touted the superior efficiency of radiant floor heat. Unfortunately, the contractor had also used foil-faced bubble wrap insulation under the slab because he had been told by his supplier that it had an R-value of 10. So the homeowners ended up (in an oil-heated house) with 200 sq. ft. of in-floor heating system directly coupled to the ground. Add some furnishings and area rugs and it's quite possible that more heat ends up going into the ground than into the room. But that floor sure stays toasty.
Response to Paul Eldrenkamp
Paul,
We all know that bad insulation keeps a radiant floor warm, supplying the "warm toes" effect that homeowners desire. Clearly, the combination of foil-faced bubble wrap and in-floor hydronic heating is a marriage made in heaven.... unless, of course, the homeowners want low energy bills.
If any readers want to more information on bubble wrap, here is the link: Stay Away from Foil-Faced Bubble Wrap.
Pure Radiant Heating
Warm toes touching a warm floor is does not involve radiation. It is conduction heating like a hot bath. But, I am intrigued by radiant heat for a reason I have not heard much discussion about. I am not sure what to make of it.
Warm air heats a person purely by conduction. A warm surface not touching a person heats the person by radiation.
People talk about a certain air temperature needed to feel comfortable. However, this is relative, depending on the radiant loss to colder objects not in contact with the person. Say the walls and the air are both at 72 degrees and a person feels comfortable. If you drop the walls to 40 degrees and leave the air at 72 degrees, that person will feel much colder. This is counterintuitive to many people because they basically perceive “heat” only as warm air delivering warmth by conduction.
The body loses heat by conduction to the colder air that touches it; and it loses heat by radiation to the colder surfaces facing it. The two mechanisms are independent. You could freeze to death in 100 degree air if the radiant loss were great enough.
What this means is that a person could live in a house that felt comfortable with an unusually low air temperature if the walls, ceiling, and floors were warmed directly and became radiant emitters. I don’t know what to make of this, but I have read accounts about how the lower air temperature compensated by direct radiant heat is healthier and more comfortable than the equivalent heat perception delivered mostly by warm air conduction as opposed to radiation.
I have no idea of how the thermal dynamics of that would shake out, or whether there would be some degree of extra efficiency by heating bodies primarily with radiant emitters rather than by contact with warm air. But I see these issues as the real mysteries of radiant heating.
Ron
Maybe Dana will comment. He has advocated using Radiant Cove Heaters, as an alternative to baseboards for exactly the reasons you suggest.
Low water temps & combustion efficiency.
Don't underestimate the improvement in raw combustion efficiency when using gas or propane fuels when it comes to radiant heating (or any hydronic heat emitter.) A condensing boiler delivering 160F water with 140F return has raw combustion efficiency no better than 86-87%, whereas operating with return water temps in the 90F range will be delivering 98% efficiency and a fuel savings in double digits, provided the thing is sized correctly for the loads.
Alex's notion that radiant floor temps “might reduce heat loss into unconditioned space if boiler and piping are located in an unheated basement, but experts … suggest that the savings would be very small at best — especially because of the additional electricity consumption to operate pumps for long hours.” is missing some of the fundamentals- and is only relevant to the non-condensing cases. The widely accepted rule of thumb regarding distribution & standby losses for non-condensing equipment is that there is about a 2-3% fuel savings for every 10F one can reduce the average boiler & distribution water temp. (Heat-purging boiler controls on high-mass non-condensing boilers can provide in the neighborhood 10-15% net saving this way.) But distribution loss & standby jacket losses are the LEAST of it when working with condensing equipment. ECM drive pumps and outdoor reset control (now standard on condensing boilers) can squeak quite a bit of efficiency out of it, provided you have the radiation that delivers at low water temperatures, despite long pumping cycles.
Whether it's "worth it" to spend the money on radiant floors & ceilings rather than higher performance building envelopes or heat pumps & photovoltaics ( PV ) is a personal judgement call. From a purely financial point of view the heat pumps & PV are already winning (and by a bigger margin every year, with the continuing steep decline in cost of grid tied PV), but even a 71F floor is perceptibly more comfortable to bare feet than a 69F floor.
But going to super-performance sub-U0.20 windows can raise the average radiant temperature of a room at about the same measure asU0.28 windows w/radiant floors in an otherwise high-R house, and in some cases would provide an equal or better uptick in human comfort.
I'm personally in the camp of spending the real money on the building envelope, not the heating systems and consider ductless heat pumps perfectly acceptable. But that's not to say people who have the money "shouldn't" be spending it on radiant floors in high-R houses for the hint of extra comfort margin t provides for the 10% of all winter hours when they would notice it, any more than I'd tell them not to spend it on granite countertops. But if they are looking at it on purely economic or carbon-footprint basis there are almost always better ways to spend the money.
I can tell all of you even
I can tell all of you even low temperature radiant floors feel very nice compared to cold cellar slabs!!!!! This is fact kids. Fact.
Radiant floors are a luxury and if you can afford them they are worthy.
No armchair pondering.... Twenty five years of feet, near the heat.
Let's say my house is
Let's say my house is ultra-tight, and super-insulated.
These are facts? These are nearly meaningless expressions.
1st Time
I've never seen radiant heated floors in my market (Houston), but I built a custom house couple of years ago and the client requested this for their master bath stone floor. We purchased from a company called Warmly Yours, installed our 1st radiant heated floor (heat strips). Last year I asked the client how they liked it, they responded very positively and said they use it year round, even in the summer when temps reach 100's and the AC's are cranked down to 68 degrees. I cringed a bit.
Response to A.J. Builder
A.J.,
You wrote, "I can tell all of you even low temperature radiant floors feel very nice compared to cold cellar slabs."
I don't doubt that. In fact, the opening sentences of my article read, "So-called radiant floors have an excellent reputation. Many customers report that this type of heating system is comfortable and quiet."
In some cases, people compare a heated basement floor with an uninsulated cold concrete floor. Of course the heated floor is more comfortable. There is a third option, however: an insulated concrete floor (with at least 2 inches of horizontal sub-slab insulation) without any hydronic tubing. Although this type of floor won't be quite as warm as a hydronically heated floor, it will be much more comfortable than the floor A.J. is talking about: "a cold cellar slab."
For those who can afford a hydronic system with in-floor tubing, go right ahead and install such a system. Others may want to consider alternative approaches that depend on high levels of insulation to achieve comfort.
Radiant Floor and Passive Solar
We completed building our super-insulated, air tight, passive solar house in Vermont 3 years ago that also included a radiant floor in the slab. While I don't have data to say how much passive solar heat gain is wasted due to the radiant floor, my educated guess would be that it is very small. I wish a sunny day in winter would give us a 20F change in temp. However, the actual change in temp to the slab, for which I do have direct measurements, is more like 4 or 5F under the best circumstances. I don't believe that a radiant heated floor given that small of a temp swing from passive solar heating is going to be much of an issue.
Martin makes some excellent points in this article. It's important that everyone knows what the reality of the situation is going to be when deciding on what heating system is to be used. I'm glad that I didn't have the misconception that a radiant floor was going to result in "warm toes" and no one should install a radiant floor with those expectations. However, I don't believe a radiant floor and passive solar can't work together under the right circumstances. In our case, we were able to do much of the labor involved with a radiant floor ourselves and same some money that way. That was not going to be the case with some of the alternatives.
The weather
At least up here in Canada the weather has provided a real challenge for systems like in-floor heat as sudden temperature swings of 20 C were not uncommon. Conversely, I find a constantly maintained temperature over 24 hours uncomfortable, preferring to keep the house quite a bit colder at night. Both situations provide a real challenge for a system with such a slow response time.
Question for Daniel
You mention that you have measured slab temperatures? What is the "typical" temp of your slab for a given thermostat setting? Have you calculated your heat flux from the slab? I'd be very interested in some real world numbers.
Wow
Wow. That is the first thought you would have walking into a basement even with the tstat set low at 60 while away. The basement I go in also has ICF walls. Amazing difference folks. Amazing. And to heat just a slab in the cellar is not tons of money in materials. This house by the way on the coldest day with my T gun is all the same temperature from the slab to the ridge 34' above. It was rigid foam insulated on the inside of framing (cathedral ceiling) and then T&G.
Good build, good performance, reasonable costs.... A PGH if you will.
response to Kent
My tstat is run from my slab temp sensor. I have found that the air temp in my tight, well insulated house is very close to the slab temp. The slab temp fluctuates less than the air temp and was advised to use that to run the tstat.
Radiant stuff
Why are radiant floors defined as radiant systems?
The heat transfer coefficient from a radiant floor is identified in ASHRAE, REHVA, CIBSE and other engineering manuals as a range between 1.63 Btu/hr/sf F and 1.94 Btu/hr/sf F. As stated , in Section 6, of the 2012 ASHRAE Handbook—HVAC Systems and Equipment, “A temperature controlled surface is called a radiant panel if 50% or more of the design heat transfer on the temperature-controlled surface takes place by thermal radiation.” The section goes on to demonstrate how and why radiant floors, walls and ceilings meet this definition. For literature support of the testing done to derive the heat transfer co-efficients published in the handbooks, see the ASHRAE, REHVA, CIBSE et al research archives.
Do radiant floors heat people?
At the long wave lengths typical of temperatures measured from skin, clothing and infloor heating, the floor does not strictly speaking “heat” the person. Rather the resulting increase in the mean radiant temperature reduces the differential temperature between the occupant’s clothes and exposed skin to the enclosure thus reducing heat transfer from the body…i.e. it’s not so much the heat you are absorbing as it is the heat you are retaining. It should also not be ignored that the air temperature in a space conditioned with radiant floors can never exceed the source temperature of the floor (exception to air heated at surfaces heated by other sources such as short wave solar radiation). This has an effect on air buoyancy and reduced stratification...from a convection perspective...its an effective way of having tepid air temperatures without causing a cooling draft.
How much energy is released from a clothed body via radiation, convection and evaporation?
For a split between latent (evaporation) and sensible (radiant and convection) heat transfer from a clothed occupant see Table 1 Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity, Section 18.4 in the 2013 ASHRAE Handbook—Fundamentals. If you can’t get your hands on the book - the radiant transfer from a clothed person represents 58% to 60% of the total sensible transfer at low air velocity and at low to moderate metabolic activities. There’s more to it than that but rather than getting into a long dissertation I suggest those interested study the materials available online.
What is the ideal floor temperature?
Thermal comfort is complex and subjective and you may as well throw in circumstantial and relative. You can't take one element of thermal comfort and make it a proxy for all the others as has been done mistakenly with air temperature in many publications and educational curriculum...and you can’t talk about any of the 10 key factors of thermal comfort in a binary language using yes/no, stop/go logic…it’s all fuzzy and gray with tones of maybe…as it relates to floors, there is exhaustive research in ranges of acceptable temperatures, and those published in ASHRAE 55 Thermal Environmental Conditions for Human Occupancy define this between 66F and 84F with the least dissatisfied for most healthy people at a nominal 75F. This is for people wearing less than 0.7 clo and having a less than 1.3 met rate and wearing “normal footwear”.
For those wearing socks or having bare feet it becomes more complicated since the flooring characteristics becomes important. For example, research shows textiles and some wood types of flooring are more comfortable at cooler temperatures (74F+/- ) than masonry floors (80F+/-).
You can study this in Fanger’s 1970 thesis and publication titled, “Thermal Comfort: Analysis and Applications in Environmental Engineering”, Olesen’s 1977 ASHRAE paper, “Thermal Comfort Requirements for Floors Occupied by People with Bare Feet”, or Chapter 9 of the 2013 ASHRAE Fundamentals Handbook.
As it relates to floor heating in terrific buildings; using 75F as the “ideal” example of a surface temperature for those wearing normal footwear (slippers for example), and a space temperature of 72F, and a nominal heat transfer coefficient (HTC) of 1.80 Btu/hr/sf F, the floor could produce a flux of approximately 5 Btu/hr/sf or well within the definition of a high performance building in a heating dominant climate.
For bare feet, as demonstrated by Olesen (1982), the measured skin temperature of low met rate occupants, the skin temperature of the feet at ambient conditions approaching 72F is approximately 77F. So relative to an 84F floor required in a traditional building with say 30 Btu/hr/sf flux, will you have the "ooh-ah" warm floor effect with a 75F floor at 5 Btu/hr/sf? Not likely - but in both cases the temperature of the floor and the perception will still be within comfort ranges provided all other factors have been accounted for…
You can play around with the variables using this simple formula:
Surface temp = (Flux / HTC) + Room Temp
Regarding “energy savings”…
There is no shortage of anecdotal evidence to “energy savings” with radiant floor heating…we’ve found everything from 10% to 100%. Within our exhaustive library of research papers none can support any thermal heating claim in a side by side residential comparison. They may exist but I’ve not read them. There are numerous modelling papers showing conservation of energy with radiant systems but these must be read with care since they are very much circumstantial. There is at least one DOE side by side residential project which demonstrated conservation in electrical energy due to the physics of circulators over blowers. At the end of the day when properly design and installed, radiant as a low temperature heating system and high temperature cooling system enables maximum efficiency from the heating and cooling plant...but this ability is not exclusive to radiant floors.
I’ve only touched on some of the discussions in this post – there are many others that need to be fleshed out– perhaps some of my ASHRAE colleagues will come forth and share their time as well.
Robert
What an informative and useful addition to the discussion. Thanks.
Response to Robert Bean
Robert,
Thanks very much for your detailed comments, and for providing technical information to help bracket comfort issues as well as readers' questions about flooring temperatures and BTU/h output questions. The information you provide is very useful.
I don't see issues of disagreement. While ASHRAE has developed its own definition of a "radiant panel," ASHRAE does not yet have the ability to prevent conduction and convection from playing a role in heat transfer in homes with in-floor hydronic tubing.
And I appreciate your explanation about the way that radiation from a person's skin to cold surfaces in a room -- especially windows, of course -- affects comfort, and that this mechanism is extremely important. While in-floor hydronic tubing can raise the temperature of surfaces in a room, thereby improving comfort, good glazing can also have the same effect. In any case, I mostly agree with your statement that “the floor does not strictly speaking ‘heat’ the person.” The exception, of course, is the famous one depicted in all the ads -- conduction from a warm floor to someone's bare feet.
I also appreciate your summary of the "warm toes" question; namely, "So relative to an 84°F floor required in a traditional building with say 30 Btu/hr/sf flux, will you have the ‘ooh-ah’ warm floor effect with a 75°F floor at 5 Btu/hr/sf? Not likely - but in both cases the temperature of the floor and the perception will still be within comfort ranges provided all other factors have been accounted for." I agree. Needless to say, many people with other types of heating systems also manage to adjust their thermostats and achieve a comfort range that works very well with bare feet.
I am also grateful for your confirmation of another point raised in the article: "There is no shortage of anecdotal evidence to ‘energy savings’ with radiant floor heating. ... Within our exhaustive library of research papers, none can support any thermal heating [energy savings] claim in a side-by-side residential comparison. They may exist but I’ve not read them."
Mean Radiant Temperatures not addressed
Excellent conversation, and having been in this industry for over 35 years, I confess that NO ONE likes to hear people call their baby UGLY. :-)
Let's start with trying to define a definition of true "COMFORT". I am sure that my interpretation of comfort is different than any other person here, because it is a subjective term. Comfortable compared to what? Living in a log cabin with poor chinking between the logs?
My definition, which I have developed over my 38 year career is fairly simple on the outside. Simply stated, being comfortable means that you are not aware of your surroundings. And it has to do with more than just the delivery of warmth or coolth. (full disclosure, Robert Bean taught me this MANY years ago, and it has served me well).
Drilling further down into my definition, you are not hot, nor are you cold. You are not over humidified nor are you under humidified. Ideally, you do not hear your comfort being delivered. Simply stated, you are not thinking about it, and if you are, then you are not comfortable. Now, all we have to do is develop a ANSI standard around this, and come up with a metric of 1-10 whereby the consumers can actually RATE their comfort feelings and their delivery system. Any volunteers?
Back to the ugly baby. While I don't disagree with Martins musings, I must say that he has not identified the one factor of comfort that has more influence over truly comfortable people. That one factor is the Mean Radiant Temperature. Simply stated, it is the temperature of those objects surrounding your body. As RB and others pointed out, and Martin confirmed, sitting next to a large glass window wall is NOT going to be comfortable under ANY reasonable air temperature conditions. It's the nature of the beast. Heat flows from hot towards cold, and our bodies can sense this much better than we perceive. And the only reasonable way to control the MRT is by influencing the surface temperatures using radiant energy, either heat OR cooling. Yes virginia, we can do radiant cooling, even in a residential setting, but that is a whole 'nother topic for a later time.
So, who built this ugly baby (radiant floor heating systems)? I like to give credit to Richard Trethewey for showing up on This Old House with a 1,000 foot roll of PEX on his shoulders and announcing to the house wives of America that they were going to do a radiant floor heating system. I consider this the kickoff of the radiant floor revolution. And boy, what a revolution it has been. The organization which i represent (Radiant Professionals Alliance) has been at it for 20 years, and there were other organizations around promoting it before that. It has the momentum of a huge freight train, and once people experience warm floors, they want it and in most cases, cost is not a consideration. After all, how can we put a price on true human comfort? Heck, we cant even come up with a metric to measure comfort… But I digress.
We, the American comfort industry have put so much effort in to promoting warm floors, that we have lost sight of the end product we are charged with delivering, that product being COMFORT. In many cases, it is NOT necessary to install 1 linear foot of tubing per square foot of living space, but we sold the consumer on the concept of "warm floors", and by golly, if their foot hits a spot on the floor that is not as warm as the rest of the space, a light bulb goes off over their head, and they think, "What did I pay $XX,XXX.00 for, and why isn't my foot landing on a warn section of floor?" You see, WE are the ones who screwed up. What the heck did we do BEFORE we had warm floors?
Hydronically, we did large surface area upright cast iron radiators, radiant ceilings, radiant walls and hot water base board CONVECTORS. (I intentionally all cap's the convectors because a very minor portion of a base board finned tube convector is delivered in the form of radiant, most of its output is truly convective energy, and this is an important part of the overall discussion.)
What I am trying to convey here is multi fold. First and most importantly, anyone who leaves MRT out of the discussion of comfort doesn't see the whole picture, and are seeing it as "heat" only. MRT drives the bus of human comfort, both as it pertains to heating AND cooling. Simple fact of life and nature.
Secondly, you can NOT manipulate the MRT in a given space using forced air, without creating even greater conditions of human discomfort, causing our bodies to go into the protective cooling mode, which I refer to as evapotranspiration. My wife refers to it as sweating… Another fact of nature that can't be changed.
So, does this mean we should throw the ugly baby out with the wash water? Heck no. I say we re-use the baby's bath water, and we redirect the radiant baby to surfaces OTHER than the floor only concept.
We need to re-educate people (homeowners, architects, designers, contractors, blog writers and a whole industry) that there is more than one way to deliver excellent human comfort by manipulating the MRT within a given space, and it can be done without having to cover every square foot of the floor with one linear foot of tubing. I strongly believe that radiant floors DO have their application, but they should be limited to those areas where people will likely be wet and poorly clothed (necked if you will), and that place is in bathrooms and walk in closets. For the balance of the areas in a given home, I can manipulate the MRT in a given space using radiant ceilings, radiant walls, sexy panel radiators, radiant towel warmers, and even an occasional radiant bath tub. We DON"T have to use floors only.
We also need to manage the consumers expectations. If we train them to expect excellent radiant COMFORT, regardless of the emitting surface, then they don't expect their floors to be perfectly warm all the time.
I own three houses, and all three are radiantly heated. I have radiant floors, walls ceilings, even radiant glass windows. Personally, I LOVE my radiant floors, but in reality, I love my radiant ceilings and walls and windows even better. It costs less to install, and it still affects the MRT, which drives the bus of human comfort. I am going to keep saying this until the world understands it...
AND, we can deliver an excellent radiant cooling comfort condition using the same surfaces that deliver warmth. WIll it require duct work, in some cases yes, but it is significantly less duct work and associated cost, noise etc because we are handling the majority of the load (sensible) with our radiant system.
This is going to require a HUGE sea change in the way we've been doing business over the past 20 + years, and its not going to go down quietly. I believe that our industry must embrace the "Good, better, best and out and out FANTASTIC" delivery of comfort. Radiant floors are FANTASTIC, and radiant ceilings, walls and panel radiators fall into the Better and Best categories, with hot water baseboard playing the roles of GOOD.
And it doesn't have to be expensive, because we are only putting in only the amount NECESSARY to counter the heating/cooling loads of the space.
For some of the best education a person can find on the internet, I ALWAYS suggest that people go by Roberts web site at http://www.healthyheating.com Play around with is Comfort Calculator that shows the effects on human comfort for a give scenario, and you will have a much better understanding of what MRT does to human comfort. It drives the bus of human comfort…
In a conversation with a PHIUS builder, he told me his load calcs came in at "5 btu's per square foot." I said per hour? he answered, "No, per year…" I said that he could heat it with the bodies in the house, to which he replied, "True, but I can't keep them there all the time, so I need a back up plan…" The "back up plan" is a perimeter radiant ceiling delivery system that runs around the exterior of the rooms, typically 2 foot intrusion into the space. It delivers the heating and cooling needs of the building here in Colorado (extremely dry air, low latent loads). Required ACH requirements are being done with an ERV.
By the way, anecdotal information here, my radiant ceilings actually make my floors "neutral" to the touch, and when at design condition, the floor actually does feel warm to me. And it FEELS wonderful, like standing in the sun on a cool fall day...
As it pertains to cost of operation, as others have noted, that is a real wild card, and even under the most controlled of circumstances, is hard to judge. But, the Canadians did a long term study, and took all of the variables into consideration, and they came up with a 12 to 15% reduction in energy consumption of hydronic radiant versus gas forced air. NOt the 30% typically quoted, but still 12 to 15% better than the competition with EXCELLENT comfort conditions. And it works excellently with ALL of the new state of the (changing) art "alternative and Green" technologies.
It is time to take our focus off of "Warm Floors" and put them back onto the delivery of excellent radiant comfort, regardless of the energy emitter. The articles and experiences are out there people, you just need to do some research…
Thank you Martin for the opportunity to express myself.
Sincerely,
Mark Eatherton
Executive Director,
Radiant Professionals Alliance
Response to Mark Eatherton
Mark,
Your reference to ugly babies confused me. Are we talking about the babies in the radiant floor heating advertisements? Or are we talking about your favorite method of space heat delivery? In any case, I think that you're the first person to call either baby "ugly."
You wrote, "As Robert Bean and others pointed out, and Martin confirmed, sitting next to a large glass window wall is NOT going to be comfortable under ANY reasonable air temperature conditions. ... Heat flows from hot towards cold, and our bodies can sense this much better than we perceive. And the only reasonable way to control the Mean Radiant Temperature is by influencing the surface temperatures using radiant energy, either heat OR cooling."
I disagree.
Assuming that we are talking about relatively new buildings that comply with the building code -- in other words, that are adequately insulated and have been built with attention to air sealing -- this issue (mean radiant temperature) is mostly about the temperature of window glass. Your drywall is basically at the same temperature as the indoor air.
So, there are two ways to influence the mean radiant temperature of your window glass. One way -- not the only way -- is to install tubing in your floor and run hot water through it.
The other way is to buy windows with better glazing. All other factors being equal, the innermost pane of a triple-glazed window will be at a higher temperature during the winter than the innermost pane of a double-glazed window.
Reigning in exaggerations
Mark Eatherton,
It's hard to pin down a definition of comfort, although I appreciate your attempt to do so.
You describe a comfortable person as someone who is "not aware of his surroundings. ... You are not hot, nor are you cold. You are not over-humidified nor are you under-humidified. ... Simply stated, you are not thinking about it." This person may be comfortable. It's also possible that this person is dead.
In other words, some people don't mind feeling alive -- knowing when they are a little warm or a little cold is not a bad thing. When I go outdoors in perfect weather, I can assure you, I'm thinking about it.
The corollary to my analysis is that Americans are so obsessed with comfort that we have raised our expectations to unreasonable levels -- to levels that are not necessarily desirable. But I digress.
You wrote, "You can NOT manipulate the mean radiant temperature in a given space using forced air, without creating even greater conditions of human discomfort, causing our bodies to go into the protective cooling mode, which I refer to as evapotranspiration." This is an exaggeration.
Not all forced-air systems result in discomfort. I assure you that a well designed, well installed forced air system will make the occupants comfortable.
If you insist that it's impossible for a house with forced-air HVAC to be comfortable, I will simply conclude that you exaggerate and are untrustworthy. Since I doubt that is the case, I hope that you can dial back your exaggerations and stick with a technical analysis of the topics we are discussing.
Martin, you need to reread
Martin, you need to reread Mark. Being an installer of radiant over twenty years ago, and understanding all your great blogs Martin I get Mark totally. Mark certainly understands the benefit of warmer windows.
Mark, we need you here at GBA. Post and help us all out with your radiant expertise. I for one will read every word and seek out your advice in the future.
I think I have already started to understand how using less but properly placed radiant is the way forward with a PGH.
I would like to hear more details as to systems used in highly insulated homes including what you call warm or radiant windows.
Aj
The ugly baby I am referring to ...
Is the use of radiant floor heating in highly efficient envelopes. You didn't actually call my baby ugly, but pointed out some obvious situations whereby radiant floors do not make sense, and I agree with most of your assertions in that (radiant floors) regards
Your assertions in regards to window glazings is true for the most part. A triple pane window is significantly warmer on the inner surface than is a double, but unless it is filled with a gas, is still going to experience mid glazing temperatures less than the 85 degree F skin surface temperatures, and will still result in less human comfort when in close proximity. Having been exposed to triple panes at design condition, I can tell you from personal experience that its not as comfy as the marketers would like you to believe it can be. I didn't have my IR camera with me, but my body told me so, and I believe that sensor first and foremost.
Then there's the whole issue about how long the gas remains between the panes with a gas permeable seal, and how do we test and verify that and blah blah blah.
The third way of influencing glazing temperatures, which you and your readers may not be familiar with is electric radiant windows. Google 'electric radiant windows' for more information on that topic. They've been in Europe for over 20 years. Although a person COULD literally heat their dwelling with radiant windows, it is NOT recommended. I keep mine (DPIGU's) in a "neutral" state, roughly around 70 to 75 degrees F depending.. I can hear rumblings in the back ground of people thinking "Why the heck would you want to put heat into an outside opening?"
Guess what, we've been placing heating elements in front of cold windows since the invention of hot water heat. And the reason we have been doing that is because the window represents the greatest (well in most cases) heat loss factor of a given envelope. The thought being, if we place a warm curtain of air between the glass and our bodies, our bodies can't "feel" the cold heat robbing condition of the cold glazing. True so long as the heating system is on, but as soon as it turns off, your body can "see" the cold surface again, and discomfort sets in.
But this conversation isn't about heated windows. Its about using radiant energy to control the comfort conditions in a given application without breaking the bank, making it compatible with solar thermal, GSHP, ASHP, woody biomass, what ever makes fluid warm. And yes, in a well built dwelling, the MRT will be higher than a non well built dwelling, but it still is the primary factor in determining excellent human comfort (or discomfort in some cases), and it can ONLY be influenced through the use/manipulation of MRT. We can argue over that until the cows come home, but it stands the test of time and mother Nature.
Thanks for continuing to educate people on this and other energy related matters.
ME
Response to Mark Eatherton
Mark,
Yes, I know about electric radiant windows -- marketed by Engineered Glass Products as "Hot Glass."
As one of the company's spokesmen, Peter Gerhardinger, has written, "Experience has shown that typical power usage [of the company's electric windows] will range from 15 to 30 watts per sq. ft., with a peak not to exceed 50 watts per square foot. One consideration in determining power usage is the desired response time. The higher the power rating, the faster the glass will warm up."
Needless to say, heat flow from a window to the outdoors is a function of delta-T. The hotter the glass, the faster the heat loss. I strongly advise readers of GBA to avoid this product.
Martin….
I know that the format of your blog/chat is probably not your design, but boy, what a pain. I want to thank AJ Builder for the compliment, and I also want to respond to your earlier response to my comment, so kludgy and all, here goes.
As AJ said, re-read my statement. I didn't say that forced air systems created discomfort. I said they they can not raise the MRT without creating conditions of discomfort. And this is a true statement. In order for forced air to significantly affect the MRT within a given space, you would have to run the forced air system at a temperature that would cause most (live) beings to break out into a sweat. I have lived with forced air, hot water baseboard and radiant heat, and I can tell you (along with millions of others who have experienced the comfort associated with radiant heating) that radiant is hands down more comfortable than the other alternatives. Forced air does get the job done, but as has been proven many times over, it is not as comfortable as a good hydronic radiant comfort delivery system. If you are comfy with forced air, that's great. But I guarantee you I am much more comfortable with hydronic radiant than can be achieved with a conventional forced air delivery system.
If it weren't there would be a WHOLE lot of people (hydronic heating/cooling contractors) looking for jobs in the other fields.
I am not sure why it is that you refuse to accept this radiant comfort fact, and really, it doesn't matter. As for being dead, not yet. Still alive and kicking, and keeping people comfortable and saving energy, as I have been for the last 30+ years.
As it pertains to radiant windows, as someone who has worked and lived and studied these gems for many years now, I can tell you that the person you quoted (Peter G.) is really not considered a reliable industry spokes person/ information source for the radiant window industry. To the best of my knowledge, they are no longer making radiant windows. (problems with their fritted/sputtered buss bars delaminating and losing continuity to the low e metallic coating.) And I would be more than glad to openly debate you on this subject, but I don't want to clutter up this thread. I can provide you with some studies and statistics that might convince you otherwise as it pertains to the efficiency and overall net effect of radiant windows. Just like anything else in life, they are not for everyone or every job, but they do have their applications. Having lived with 14 of them for the last 5 years in two of my homes, I can tell you that they are extremely comfortable. Imagine pumping sunshine from the sun (PV panels) through wires into areas where the sun never shines (North facing windows). The numbers Peter is quoting are numbers that were extrapolated from the reach in freezer door industry standards, and are MUCH higher than necessary to maintain the glass in a thermally opaque, or neutral condition. In any case, if you are open to it, I am more than willing to discuss, and debate with you on any subject relating to the radiant world.
Thanks for continuing the conversation and allowing me to contribute to your forum. I am not here to blow smoke up peoples skirts. I am here to help educate.
ME
The vortex...
I can feel I’m getting sucked into the vortex…my last post…have work to do [:@).
Re: MRT, window and drywall temperatures and comfort
Part II: Mean radiant temperature (MRT) integrated with dry bulb (tdb) obtains in thermal comfort analysis the “operative temperature” (top) or what people actually sense.
Consider top as the fulcrum on a teeter totter where on one side you have tdb and the other MRT. To maintain an acceptable top in the presence of a dropping tdb the MRT must go up; or you can say in the rising of a tdb the MRT must go down. This is in part, the theoretical basis for the lower thermostat setting argument which is true in theory practiced by some but not all (what else is new?).
When does the temperature of the drywall equal the air temperature?
ASHRAE Handbooks do not address this specifically from a comfort perspective but the ASHRAE 55 Standard does provide a litmus test for when the MRT can be assumed to be approximately equal to the air temperature. Ergo if using ASHRAE Standard 55, the window has to be incorporated into the analysis. Before defining when the tdb can be assumed to equal the MRT for a designed operative temperature, readers unfamiliar with inside surface temperatures of glass should have a first look at Table 2, Indoor Surface Heat Transfer Coefficients, 2009 ASHRAE Handbook of Fundamentals, Chapter 15, Fenestration; or for more detailed reviews use the LBNL Window Software.
If you can’t get access to the tools; as per Table 2 examples, under no solar load, the inside surface temperature of triple pane, ½” argon filled between panes, 0.1 E on surfaces 2 and 5 with an outside temp = 0F and an inside temperature = 70F, the inside glass temperature is ≈ 63F; for double pane, 0.1 E on surface 2, the inside surface temperature is ≈ 56F.
At approximately 72F ambient temperature, the mean skin temperature is approximately 88F, so the differential between the body and glass becomes the motive force for drawing energy away resulting in the sensing and perception of cooling. This is only part of the story since the area of the glass, exposed skin area, characteristics of the clothing, geometric orientation of the person to the glass etc. etc. etc. are all non trivial elements to be considered.
… back to….when can you assume the tdb = MRT?
The basic ASHRAE Standard 55 test is tdb = MRT if Uw < 15.8/(tin-tout)
This says if the U-value of the zone enclosure (weighted average of all surfaces including windows) is less than 15.8/dt then you can assume the air temperature is approximately equal to the mean radiant temperature. Caveat…this is a very simplified test and is under review by our SSPC 55 Committee. In my own practice, it is only used as a starting point not as a definitive conclusion.
Nevertheless, readers should reflect on the window performance and its area, the wall performance and its area plus the outside design conditions because only the right combination can deliver a yea or nay assumption for tdb = MRT.
In detailed studies of MRT, the occupant’s geometric relationship to the window is considered - as it should be for accuracy since the closer the body to the critical surface the greater its affect on the sensation and perception of comfort. This principle holds true for all radiant surfaces. See UC Berkley, Center for the Built Environment and papers on thermal comfort and windows.
For those with spare time and like to play with Excel, it’s really a good exercise to do a simplified calculation of the space MRT, using an area weighted average of the surfaces in a hypothetical space playing around with framing factors, wall and window performance and window/wall areas and watch what happens. It’s not difficult math and if it matters at all to some, a seasoned designer should be able to perform the calculation anyways to demonstrate compliance with comfort Standards.
As another exercise, take the same hypothetical space and move it around the country and watch what happens in Fairbanks or Seattle or Montreal or New York…not the same beast.
You can model this topic in 2D using the ASHRAE Thermal Comfort Tool and soon you will be able to model it in a 3D space using the ASHRAE 1383 Radiant Modeler.
How does this fit in to the topic at hand?
Radiant heating and cooling is a tool just like any other tool…in the hands of a skilled designer on the right projects with the right clients it can be an elegant way of conditioning people and spaces – and yes as Mark and others can verify it can even be low cost and simple…in the wrong hands...well…don’t we all know the rest of that story …[:@).
Best of luck with the rest of the conversation...
Response to Mark Eatherton (Comment #43)
Mark,
You wrote, "Forced air does get the job done, but as has been proven many times over, it is not as comfortable as a good hydronic radiant comfort delivery system."
I suspect that our disagreement is unresolvable, but I will put forward my arguments to GBA readers and let the readers reach their own conclusions.
Many advocates of in-floor hydronic tubing compare the comfort provided by these systems with run-of-the-mill forced-air systems. As GBA has reported for years, most forced-air systems in the U.S. have oversized furnaces, undersized ductwork, leaky duct seams, and lengths of ductwork installed outdoors (in unconditioned attics). These badly designed, badly installed forced-air systems often have comfort problems.
However, a forced-air system with a properly sized furnace, properly sized ductwork, sealed duct seams, and with all ductwork installed in the conditioned space is an entirely different animal. GBA advocates that readers should install the latter type of forced-air system, not the former.
Forced air, done right, is comfortable. Mark, if you tell me that you are uncomfortable in a home with a well designed, well installed forced air system, I'm going to assume that we are talking about a princess-and-the-pea problem. A certain percentage of the population is never comfortable.
This issue is similar to the debate in Maine between Passivhaus advocates and Pretty Good House advocates. Is a properly designed, properly installed forced-air system "good enough"? Or is it too uncomfortable? I'll leave that for GBA readers to determine.
Response to Robert Bean (Comment #44)
Robert,
Once again, I am grateful for the technical information you have shared to help our readers bracket these problems.
Once we have finished looking at our spreadsheets, however, we have to return to our living rooms and determine the best way to stay comfortable at a reasonable price.
You noted that when the outdoor temperature is 0°F, the inner pane of triple-glazed window will be 7°F warmer than the inner pane of a double-glazed window (63°F instead of 56°F). What does this mean in real terms? For the vast majority of homeowners, the difference in comfort is significant. If you live in a cold climate, you are far more likely to be comfortable sitting next to a triple-glazed window on a cold night than sitting next to a double-glazed window -- no matter what type of heating system you have.
For most of us, this choice of a triple-glazed window tips the room from uncomfortable to comfortable. As I wrote before, the "mean radiant temperature" issue really boils down to windows. (If your skin is made uncomfortable because of radiation from your skin to the Sheetrock on your walls, something is seriously wrong with your walls. For any code-legal building, you won't have radiational cooling problems with drywall. As I said, this is a window issue.)
For a small minority of Americans and Canadians, it's possible that triple-glazed windows and a 72°F thermostat setting aren't enough. They want in-floor hydronic tubing. I say, "Go right ahead and install it if you can afford it."
However, I suspect that the uncomfortable Americans and Canadians have problems with their thermal envelopes, not their heating systems. The reason they are uncomfortable is that their homes have air leaks, insufficient insulation, or cheap windows.
Very few Americans and Canadians have experienced living in a house with a good thermal envelope, so they don't believe it's possible to be comfortable in a home unless the entire floor is heated with circulating hot water. There are simpler solutions, however.
Martin you keep sliding and missing and repeating
First Martin, it has been mentioned by Mark that less radiant can be installed in homes that are highly insulated and well sealed. Michael Chandler and I both advocate using less radiant in a modern highly insulated home. Stop comparing "heating the whole floor" to anyone suggesting doing so in a home that is highly insulated. NO one is advocating for that Martin.
And yes if one spends to buy a very good hot air system with variable speed expensive furnace and the best duct work then those systems are very nice. Average homes do not have these systems. We contractors that build custom homes do have customers who afford high end homes and buy much more expensive HVAC systems than most have so that they can have luxury comfort. We have around here many homes that have both radiant hydronics, GEO, hot air and more all in one home. I just passed along a job for a home where the HVAC remodel price must have been near $200,000.
Radiant has it's place. No one has to have any radiant. But even lower cost homes can enjoy a few square feet of heated tile in a master bath for a cost of $5.00 a month... if they choose to buy that EXTRA COMFORT.
I build for a endless variety of people. We talk over the plans and design, and they decide what they finally want and that is what I build.
I could see someone enjoying a heated window in a specific view window by their favorite reading lounge chair....
Martin, I do love your knowledge, don't take this post wrong... but there is room in this world for Marks and Roberts and even ajs.
aj
Response to A.J. Builder
A.J.,
If your customers are happy with these systems, that's great. I have no problem with anyone installing this type of heating system if that's what they want.
For other GBA readers who are debating the pluses and minuses of different heat distribution systems, however, it's possible that the information provided in my article is useful.
Martin, if your blog read
Martin, if your blog read like my last post 47 it would be up to date and useful to all whether they desire radiant or not. Just harping that it is not worthy is wrong. Doing a whole home in radiant with 6" spacing is what we used to do and that is wrong. Mark and I and Chandler and you Martin say to avoid whole floor radiant with a lowly insulated home. So we all agree. My point is your blog is old news and not properly up to date.
I can't explain my points any clearer... next blog.
aj
Response to AJ
AJ,
I'm glad we all agree.
For many readers, the points made in this blog probably are, as you say, old news; but for some readers who are just beginning to think about these issues, the information may still be useful.
Old news, Too Late.....
Well, I for one could have used this new to me "old news" a little sooner.
Kent,
I am building a shop similar to yours. Mine is a two story 1400sq per floor, bank barn style.
I used twin wall clear polycarbonate panels in the basement roll up doors, instead of going with a typical insulated metal panel.
I also used 3" XPS under my slab, and around the entire structure from the footing up to the eves. I am planing on flash and batt before finishing the interior But have not got to that yet. I also do not have any insulation in the cathedral roof yet, not sure how to proceed with that part..... Nor did I have any windows or doors on the main floor.
I only put this info here as I do not have the math knowledge to figure out my heat loss in this structure, and admire those that do, but it must be substantial.
The basement slab and the concrete main floor I put in HePex spaced every 6",,, DANG, could have saved some cash there.
This winter, ( I am in South Ontario) I had a case of bottled water sitting on the basement floor and the bottles in the middle of the case never froze. It was sitting about 4ft from a freezer I had running in there, which was between the two roll up doors.
The winter sun shines about half way to two thirds of the way into the basement through the poly doors. And other than the electric freezer, there was no other source of heat this winter. So, apparently there is substantial solar heating through the doors into the concrete floor. DANG, didn't need the radiant tubes in the basement at all.....
So, not having any experience in designing or using a radiant system, I was sold on it by clever marketing of energy saving claims. Personally, I wear socks, so warm bear feet is of no concern.
However, I have concrete countertops at home, and the one I am sitting at now typing this makes my arms cold. I keep the house at 18C. 16 when at work and at night. As the counter top is in the middle of the room, I can only assume it is also 18C. But it still makes my arms FEEL cool. And often I wish I had added some electric heating to the counter when I built it.
So, I have no illusions that the shop floor, (may become my house one day) will FEEL toasty warm like my wood stove dose.
BUT.. What if the concrete counter I sit at, was the only radiant emitter in my house. It would have to be maybe 10 or 20 deg warmer than the desired air temp to keep up with the heat loss of my century home. Obviously that wouldn't keep my house warm enough without burning my arms.
So, could you not put the in floor radiant only where people walk. The bottom of the kitchen cabinets and under the living room furniture need not feel warm, Neither dose under my bed. I was given advise to put an extra pex run around the perimeter of the slab as thats were it would loose heat to the outside, but mine is insulated with 3" of xps on the outside.... And even if it was not, why,, Thats not where I want to feel the heat.
Why they put the heat registers under windows also doesn't seam right, why put the heat closest to where its going to leave.
So, I for one, am grateful for the info, Tons of really good posts on this one, WAY more math than I or most people I know could understand, but good to know someone out there actually measured these things
Heating and Cooling with Tubing in Floors
Hello Martin,
Thought I would weigh in with a side bar. You should pay a visit to my home in Maine, where I have a geothermal system with radiant floors, and I both heat and cool the house with the radiant system. During the winter, the COP on the geothermal system is in the 5 range, and during the summer, it is off the charts. We call it "free cooling", as I am simply running two small pumps to a plate heat exchanger, and that provides cooling. I also have an HRV with a ground-source coil for pre-heating and pre-cooling/dehumidification, and a Italian made hydronic boosted dehumidifier to manage the humidity in the house. My electric bill in June-August the last two summers was less than $50/month, and the house stays at 75F/60% humidity all summer. Using hydronic ceiling systems with heat pumps for heating and cooling is growing rapidly in Europe. So the arguments are changing. :-)
Response to Barry Stephens
Barry,
And what was the total cost to install your HVAC system, including heat distribution and cooling distribution systems?
True Radiant Heat
I have long been intrigued with the principle that a comfortable sense of warmth can be achieved by reducing air temperature while raising radiant temperature. I believe this is one of the least explored concepts in home heating.
And I think that is due to the fact that radiant transfer is the least understood of the three heat transfer mechanisms. Even the so-called radiant floors are mostly understood in terms of their conduction rather than radiation, as indicated by the universal reference to warm toes. In fact, I would speculate that the majority of comfort perceived from a warm slab is not the warm toes, but rather, the radiant transfer to peoples’ clothing and directly to their bare skin. It is just that the perception mistakenly interprets the comfort exclusively as the toes which are being warmed by direct conduction.
I believe that this is one reason why people think warm floors are the only means of radiant heat. In other words, radiant heat has erroneously come to mean heat transferred by direct contact, which is actually not radiant heat. It is conduction heat. And therefore, according to that erroneous belief that interprets radiation as conduction, the so-called “radiant” emitter has to be a floor. Actually, a radiant emitter could just as well be walls or a ceiling.
Response to Ron Keagle
Ron,
People have been building hydronic radiant walls and ceilings for many years, and the GBA Encyclopedia mentions this approach in the article on Hydronic Systems:
"Those who don't like looking at baseboard radiators may want to consider the installation of hydronic wall or ceiling panels. Most are surface-mounted, but they also can be embedded behind finish materials. They're durable as well as out of the way. The main disadvantage is higher cost."
Proven Concept Prototype Hydronic Radiant Floor Heating/Cooling
After reading "All About Radiant Floors" and the 50+ follow-up blogs, it seems clear to me that those who have done it, get it and those who haven't are merely opining (to say the least).
The following is an abstract for a conference presentation this summer:
Real World Performance Results of the Prototype S.E.E.D. Home™ with Stand-alone Hydronic Radiant Floor Cooling & Heating, and previously test-monitored by DOE Build America Program engineers.
Inhabited for over two years during all seasons of weather, The S.E.E.D. Home™ (Super Energy Efficient Design) has shown that its high performing thin shell full circle solid insulated thermal envelope coupled with its temperature controlled finished concrete floor via a closed loop hydronic radiant floor heating AND COOLING comfort system, seasonal dehumidification, whole house filtered fresh air ERV and ceiling fan air movement (for subtle cooling breezes) provides cost effective year round thermal comfort with exceptional indoor air quality and near net zero operation – No active forced air system; No hot and cold air drafts or varying micro climates; No recirculated stale indoor air. The S.E.E.D. Home™ design-build premise was based on the proverbial KIS (Keep It Simple) principle and, from a practical perspective what it would take to design and build (methodology and product choice) the most energy efficient home under 2000 sq.ft of living area; What would the installed costs be and how would they compare to others, but always with the most energy efficient measures being the choice determinant first and foremost. Having been tested and monitored via embedded sensors by DOE Build America Program engineers and inhabited passively and experimentally by the designer/builder, real world results have produced beneficial consequences far beyond what was originally thought. With eight (+/-) hour NONSTOP air to water air source heat pump compressor operation and system OFF for sixteen (+/-) hours, heretofore unattainable operating efficiencies have been achieved: NO compressor short cycling; optimal overnight (best electric utility rate) summer operation, daytime winter operation and almost no spring or fall operation.
There is a lot more that has been gleaned from this project that has disproved so much of the 'expert' conventional thinking about hydronic radiant floor comfort systems.
The S.E.E.D. Home design premise was very straight forward and simple: design/build a house like an ice chest (full surround solid insulation) and utilize the entire entire concrete floor as a controlled active thermal mass storage and delivery medium; like blue ice except the floating slab is 'plugged in' via hydronic loops to an air to water air source heat pump that provides the 'hot' and 'cold' for determining the floor temperature.
If you have ever been in a cave, you have a sense of what it is like: you are enveloped by consistent and constant thermal comfort hovering around 75Fdegrees 24/7/365.
From this proven concept perspective, I (for one at least) know for a fact that hydronic radiant floor heating AND cooling works, works extremely well, and does so without an active forced air system.
We hope and plan to scale this in the near future.
UFH do you live with it?
I wonder how many of the people who have comented on this, have actually designed, installed and lived with UFH?
When you build a home with UFH, you turn on the heating the moment you move in and turn it off when you leave........It is best left on 24/7.
When you have UFH, after a while, you forget you have heating, because it goes un noticed, it just works, keeping you comfortable, the rooms are warm and comfortable 24/365. The air never feels too warm or too cold.
UFH does not need to be pex in concrete. Concrete is very slow to heat, and even slower to cool.
Go for light weight UFH, pex laid in channels on top of sheets of polystyrene or similar closed cell insulation.
A six inch thick layer of polystyrene and pex covered by fully floating oriented strand board flooring gives you the best heating system. Where you have large floor to ceiling picture windows, the UFH deals un noticed with the cold air dropping down the glass. And there is nothing to spoil the view.
Keep in mind that water is quicker to heat quick and to cool than concrete.
Water is 4,000 times better at delivering heat than dry air. It is quiet in operation, very little air movement, it will keep your feet un noticably warm on the coldest night. The floor surface temperature will normally be in the region of 24 to 27C. But how warm is your choice.
The temperature of your foot is about 30C, the UFH is lower than that, but not low enough to allow cold feet.
UFH is best when it is zoned. Zoning means each room can be just as warm as you wish, with a really warm bathroom in winter. Zoning means economy, why have a room too warm when it can be perfect.
UFH means you can have two or more zones in a room, perhaps you and your lady like different temperature, with wireless zoned control, you can sit the thermostat on a coffee table by your side and have the perfect temperature, as can your lady, with her own thermostat. No more fighting as to how warm or cold the room should be.
With UFH there is less heat loss through the walls due to high temperatures between the wall mounted radiator and the wall.
Much cheaper to run as you decide just how warm each room will be and you move seamlessly through the year from summer to winter to summer.
Response to Michael Ginsburg (Comment #56)
Michael,
You wrote, "it seems clear to me that those who have done it, get it and those who haven't are merely opining."
One of the reasons that I included a long case study in my article (about the house in Colrain, Massachusetts) was to provide a real-world perspective from an actual project. The designers of the house in that case study concluded that they wouldn't use in-floor hydronic tubing again.
Clearly, this type of heating systems works well in homes with high heating loads. Occupants of these homes are almost universally satisfied with their heating systems.
What many people don't realize -- including you, perhaps -- is how low the heating loads are in a well designed, well insulated house with a low rate of air leakage. Many superinsulated homes have design heating loads of 10,000 Btu/h or less, even in a cold climate. These homes don't need in-floor hydronic tubing.
The number of Passivhaus buildings in the U.S. that use in-floor hydronic tubing for heating is very, very small.
Response to Roger Anthony (Comment #57)
Roger,
Although you don't explain what you mean by U.F.H., I'm guessing that you are referring to "under-floor heating."
Unlike you, I don't think it is an advantage that with this type of heating system, "You turn on the heating the moment you move in and turn it off when you leave. It is best left on 24/7." The fact that some of these heating systems require circulators to run for 24 hours a day can lead to high parasitic energy loads. This 24-hours-a-day problem was one of the reasons why Robb Aldrich was unhappy about the high electricity usage of the hydronic heating system at the Colrain house.
If your house has a great many "large floor-to-ceiling picture windows," as you describe, you may end up needing an expensive heating system. However, I prefer a different approach: one that specifies smaller windows and a much tinier heating system.
By the way, Roger, your description of the typical family that you imagine yourself writing for -- "you and your lady" -- is the type of language that advertising copywriters used in the 1950s. It's time to update your assumptions.
A few thoughts
Fascinating stuff. Maybe I went to a poor architecture school, or maybe I just wasn't listening, but this is all new to me.
It seems to me that the two camps are talking at cross purposes. The Radiant proponents are championing the comfort it provides, the sceptics see it as a poor choice once you have already decided to build your envelope to a more exacting standard. There doesn't seem to be much debate that it provides a very nice living environment, but how this fits in with any aims of efficiency hasn't to me anyway been sufficiently addressed.
Would the choice make more sense if the initial outlay was a lot less? Are electric radiant cove heaters an option or is their poor efficiency as compared to say mini splits still too much of an issue?
Robert: I'm not sure I understand how UFH can practically zone a single room so the occupants, even if they stayed stationary the whole time, would experience distinctly different temperatures. Could you perhaps elaborate?
Response to Malcolm Taylor
Malcolm,
Q. "There doesn't seem to be much debate that it provides a very nice living environment."
A. I agree.
Q. "How this fits in with any aims of efficiency hasn't to me anyway been sufficiently addressed."
A. I tried to address this issue in my article. There is no evidence that these systems save energy. A BTU is a BTU, no matter how it is distributed.
Q. "Would the choice make more sense if the initial outlay was a lot less?"
A. Yes, I think it would. But these are expensive systems, and they don't make sense for low-load houses.
Q. "Are electric radiant cove heaters an option or is their poor efficiency as compared to say minisplits still too much of an issue?"
A. Electric radiant cove heaters are electric resistance heaters with a COP of 1.0 compared to minisplits which have a COP of 2.5 to 3.5. Electric resistance heat is expensive to operate in most locations, but may make sense for very well insulated homes, especially if local electric rates are low or the house is equipped with a large PV system.
Q. "I'm not sure I understand how under-floor heating can practically zone a single room so the occupants, even if they stayed stationary the whole time, would experience distinctly different temperatures."
A. It can't.
Zoning a Radiant Floor in One Room
As I understand it, a radiant floor in a single room could be divided into two zones of floor area with each one presenting a different temperature. A person would feel an increase of temperature when moving out of the cooler zone and into the warmer zone and vice versa.
However, the warm floor zones would each heat air by conduction in addition to their radiant transfer, and the heated air would rise in convection. So the heated air from the two zones would mix and evenly distribute within the room. So the division of the two zones would not extend to air temperature.
And also, the rising warm air, mixing to a uniform temperature, would also heat the ceiling to that uniform temperature. Then the ceiling would radiate a uniform level of radiant heat back down to the occupants regardless of which floor zone they were in.
Response to M. Taylor and M. Holladay
There has been some significant research, field testing and monitoring by the Dept. of Energy Building America Program in the last few years which has provided valuable, practical and published results that has provided new insights into the proactive comprehensive benefits of this comfort system. Embedded sensors and more than two years of real world testing, monitoring, experimenting and experiencing has shown enormous benefits to hydronic radiant floor heating and cooling.
Current published research negates much of the historical assumptions about hydronic radiant floor comfort systems especially with regard to the questions Mr. Taylor asked. Specifically:
1) agreed, there is no debate about the benefits: having consistent, even temperatures throughout the home is a given with this system and, I might add, this is accomplished without an active forced air system that inherently produces varying micro climates on a regular basis (30 minutes or so) because of system cycling.
2) Yes, there is real world evidence that a well planned radiant system produces beneficial ROI for financial, health and comfort.
3) Does granite cost more than laminate? Do LowE windows cost most than single pane windows? In fact, it makes the most sense for low load houses that have been designed with a whole house system approach.
5) Individual room or area zoning is simple and easy. However, it is mostly unnecessary because /ambient temperatures always hover around 75degrees, 24/7/365.
Had Mr. Holladay read beyond the first sentence of blog #56, he would have become aware of some important current research into this topic.
Response to Michael Ginsburg
Michael,
I have no doubt that homes with this type of heat distribution system are comfortable.
The fact that in-floor radiant heating has been studied by researchers is no surprise to me.
These systems make sense for a home with a high heating load. But you have not provided me any reason to change my conclusion that these systems aren't appropriate for low-load buildings.
Response to Mr. Holladay
Nor have you asked, but I will assume this was an inquiry.
If there is a high heating load than there obviously a thermal envelope problem and this would require non stop heating to be comfortable. This would obviously mean continuous operation of radiant floor circulators (expensive) or constant cycling of a forced air system (expensive and annoying).
With a low heating load, such as confirmed in The S.E.E.D. Home research, the air to water air source heat pump operates during the daytime only for a few hours and that's it. No operation during the evening or overnight when temps are the coldest and peak load demand exists. Operation occurs during the warmer daytime hours for heating and overnight hours in summer for cooling. This operating methodology provides significant benefits comfortwise and even more so importantly financially. When compressors employ constant operating modes, there is NO short cycling, ever. Additionally, time of us operation provides utility rate reductions in winter (with only daytime operation) and in summer with only overnight operation.
Michael
I have no fixed opinion one way or another. I'd like to be be to make an informed choice, You describe "the proactive comprehensive benefits of this comfort system", and I must admit I can't begin to understand what that even means.
I'm sure you don't intend to be obscure, but your posts seem to boil down to: "Of course it works, evidence is everywhere, why don't you just listen to me", without even pointing to anything I can use to make my own assessment.
Again, I'm quite willing to be convinced, but need something more than a sales pitch.
Response to M.Taylor
Sorry, I don't mean to sound like a sales pitch.
Please read blog 56 above to get a better sense of what comprehensive high performance energy efficiency is about.
The Dept of Energy Building America Program (http://energy.gov/eere/buildings/building-america-bringing-building-innovations-market) has for the last few years (along with many other entities) been majorly involved with advancing energy efficiency in new and remodel construction, best practice research and related things.
The S.E.E.D. Home prototype project was an 'outside the box' approach to seeking maximum energy efficiency in a newly constructed home under 2000 sq.ft. of living area. When research engineers from the DOE Building America Program learned about the intended effort they very much wanted to partner with the designer/builder before, during and post construction to assist with radiant design and testing and monitoring it with embedded sensors for a couple years.
There are several published and still to be published reports via DOE BAP as well as conference abstracts describing and assessing the project.
Comfort
The common perception of what a heating/cooling system is, is wrong. That perception being, that a heating system is to heat a house and a cooling system is to cool a house. It is easy to see why people think this way. That's the only thing that makes sense, right?
The reality is, a Comfort System (heating/cooling) has one purpose only! That is to create an environment that accurately controls the heatloss from our bodies. Robert Bean has explained this in great detail as has Mark Eatherton. Our bodies produce much excess heat which will be removed in three ways, radiation, evaporation and convection. Conduction losses are small enough to generally considered irrelevant. Such being the case, any comfort system needs a 3-pronged approach to try an achieve the most ideal environment to absorb the bodies heat losses. The temperature of all the thermal mass that surrounds you should be controlled very precisely as this controls the radiation heatloss from the body. Your body will sense as little as °F difference in the temp of the mass surrounding your (MRT). At least mine does! This is the biggest part but there are 2 more. We still have air temp and humidity. If the MRT is at a desirable level, the air temp will be in close proximity, unless one has a leaky house. Humidity levels should also be considered and different actions need to be taken depending on what part of the country you live in.
So now. The discussion of whether a Radiant system or a forced air system will best achieve these goals in a well insulated house. A Radiant system will maintain a stable MRT and by default keep air temperatures at an acceptable comfort level.
On the flip side, trying to maintain comfort by using only air and humidity, will prove a much harder task. Even a super insulated house will have conductive heat losses through all the exterior skin. Lets follow the heat movement. Heat always flows from high temperature to low temperature. The source of the heat is warm air in the room. In order for that air to cool off it will have to transfer to a colder surface, that surface being the inside skin of the exterior walls. Air is not very efficient at giving up it's heat to a solid object, such as a wall. The best way to get air to make a sensible heat transfer, is to have a large temperature difference and a large surface area. And so, the sensible heat transfer from the air to the walls must happen at the same speed as the conductive losses through the walls therefore, it can be easily understood that the interior surface of the wall will be at a lower than desired temperature for this to take place. As it gets colder outside the losses speed up and the interior surface of the walls drop even lower. This must be true because we know air transfers it's heat slowly and now your furnace is running more. The only way the extra heat can escape that fast is if the surfaces of the walls are that much colder. Look at where we are now with our three pronged comfort approach. Your core temperature is up and your head might feel a little thick and lumpy due to overheating. At the same time your extremities feel a little chill. That is because your bodies heatloss is no longer properly balanced due to a higher air temp and a lower than acceptable MRT.
Controlling the MRT is of the utmost importance and to this point we have found Radiant to be the best vehicle to achieve this goal.
If you still have doubts, I suggest it's time to start your studies. I am sure you will reach the same conclusion. Those who have the desire to learn will find that the truth can not elude them for very long.
Wishing everybody the best.
Harvey
Michael, you link goes to
Michael, you link goes to Building America but NOT to an article to support your posts.
Misconceptions abound
Martin ,
I think this discussion and some of the systems and studies you reference should be looked at for what they most likely are . Bad designs and poor installs using antiquated theories and misconceptions about radiant floors . Just as you mentioned poorly designed and installed ducted systems I will respond that unfortunately the hydronic heating world is also chock full of guys that should not heat a dollhouse with a blow dryer , this is sad but true of both sides of the coin . This can be proven in both markets , I design and install comfort systems and when I perform this task in a remote market from my location the hardest and most tedious part of my job is vetting contractors who will do as I say and not as they have been taught , this would probably be true of an esteemed gentleman from Az whom we both are aware of .
Radiant heat can be designed and installed in ANY home no matter it's construction and it can be done competitively when all things are taken into account . I assure you that your Passivhaus standard is no different in the fact that a radiant system can be designed and installed that will both be efficient , cost effective over it's lifecycle , and provide superior comfort . Martin , all you need do is find a truly competent designer who possesses a true understanding of heat transfer and all its' intricacies and who is not reliant on product based manufacturer training to achieve what you call impossible and a waste of effort . Not everyone is constrained by the BOX of which you speak . Some of us understand that less is more and mass has for the most part been residing at the wrong address and the emitter has been placed in the wrong area . There are at least 3 men whom have commented here that know exactly what I speak of , 1 of which has recently had to tone down his passion , you know who you are .
So how do you get all the ductwork within the envelope Martin ? It must also cost more to pay a truly competent man to design and install properly a ducted system . Real radiant designers and installers will cost less on average than guys whom do not appreciate that less is more and will install what each differing envelope requires .These are truths . Fact of the matter is that when you start doing real accounting on the extra time and material spent to bring these less than desirable systems inside the conditioned space to make them what they aren't the price difference becomes negligible .
My wet house that is 2 stories tall where the occupants desire 9 foot ceilings can be 20 feet tall to the top of the second story , so can yours but to do so you will have to insulate the attic and address all those issues or build numerous bulkheads and or soffits to enclose ductwork that will still have 3% leakage , all these things cost money and must be considered in the cost of the ducted system . These costs are always overlooked .
This whole discussion reminds me of an Upton Sinclair quote "It is impossible to get a man to understand something when his paycheck depends upon his not understanding it " . Please tell me this man is not you and that you are one of the few that has open eyes and an open mind .
Respectfully ,
Rich
Michael
My post to you inadvertently read like I was demanding you come up with something to convince me - which of course you had no obligation to do. Thanks for the reply.
Response to Michael Ginsburg (Comment #65)
Michael,
You wrote, "Time of use operation provides utility rate reductions in winter (with only daytime operation) and in summer with only overnight operation."
In theory, a low-load house with adequate interior thermal mass can use this heating and cooling strategy (only operating cooling equipment at night, and only operating heating equipment during the day) regardless of the type of heating or cooling equipment installed. This method of operation has nothing to do with in-floor hydronic tubing.
It's important to point out, however, that very few residential customers in the U.S. are offered time-of-use billing for electricity, so this method of operation mostly benefits electric utilities, not homeowners.
Response to Harvey Ramer (Comment #68)
Harvey,
It is condescending to assume that I don't understand the basics of "mean radiant temperature" or the fact that humans can feel uncomfortable when heat radiates from bare skin to cold surfaces in a room. (As I have written many times, these cold surfaces are usually windows.)
In a poorly designed, poorly insulated, poorly constructed house, it is certainly possible for occupants to be uncomfortable. There are plenty of badly installed forced-air systems in homes with single-glazed or double-glazed windows; in such a home, it's easy to be uncomfortable. (There are uncomfortable homes with hydronic systems as well.)
However, after all of the mumbo-jumbo about mean radiant temperatures has been explained -- and trust me, I know what you're talking about -- the question remains: will the occupants of a superinsulated home with a low rate of air leakage be as uncomfortable as you imply if they choose a different heating system -- say, two or three ductless minsplits, or a small well-installed forced air system?
The answer is no. We know the answer, because thousands of superinsulated homes have been built since 1980, many without radiant floor heating systems. And the occupants of these homes rave about indoor comfort levels.
The key to occupant comfort is reducing air leakage rates through the thermal envelope; installing above-code levels of insulation; choosing high-performance windows; and doing a good job of designing and installing your heating and cooling system.
Occupants of homes with in-floor hydronic tubing are very comfortable. But it's absurd to claim, as you apparently do, that occupants of homes with other types of heating systems are necessarily uncomfortable.
Response to Richard McGrath (Comment #70)
Richard,
I agree with most of your comments. You're right that it is difficult to find an HVAC contractor who can do a good job of calculating heating and cooling loads, sizing equipment, and installing a forced-air system.
It can also be difficult to find an HVAC contractor to do a good job designing and installing a hydronic system, as you explain. (As you point out, "the hydronic heating world is also chock full of guys that should not heat a dollhouse with a blow dryer.")
This is a big problem for the residential HVAC industry, and GBA has been doing its best to help educate readers, in hopes of raising the bar for the industry, for designers, and for homeowners. I'm sure that you are contributing to this effort as well.
The only point of disagreement is whether a properly designed, properly installed heating system with in-floor hydronic tubing will be a cost-effective choice. You say it will. I say it won't, because it will cost significantly more than other options.
Response to Harvey Ramer
Harvey,
I like your explanation, and I think you have hit upon a fundamental point regarding the difference between radiant heating and warm air heating in terms of the human perception of how one’s body feels when being heated by either of these two mechanisms. I would like to focus on this and ask a further question.
Of course, the two mechanisms will always be operating together as a blend because radiant surfaces will heat air and vice versa. But say you have a room in which a person feels comfortable with an air temperature of 72 degrees F., and some given radiant temperature of the enclosure which is affecting that person. So the air temperature and the radiant temperature are collaborating to provide a sense of comfort to the person through their heat transfer.
Now, say that you increase the air temperature to 78 degrees F., and decrease the radiant temperature to compensate, so you are still delivering the same total amount of heat to the person. Will the person still feel the same way in terms of thermal comfort? If not, why not?
Here is another variation of the question: Does a btu of heat delivered to a person by radiation have exactly the same effect on the person as a btu of heat delivered to the person by conduction from the contacting air?
Martin
I'm sorry if I sounded condescending to you. It was not my intention. I prefer to write my posts in such a manner that those not as well versed in our industry will have a better comprehension of the physics behind a comfort system.
One must realize that comfort is the perception of an individual. So if a person moved from an average house with forced air to a super insulated house with forced air, their comfort level will go up, due to the increase in MRT, and they will no doubt rave about it. After all, it is likely the best comfort they have had. Even still, the comfort they now experience can be further improved through precise control of MRT. Best delivered through a radiant system.
Again, MRT is the largest and most important factor in a persons heat loss and should never be ignored. While a triple pane window is an improvement, the interior surface will still have a lower MRT then is desirable.
If anybody would like to do an experiment at home, here is an easy way to experience the difference MRT makes. If you have a forced air system, go to your thermostat and move the fan selection from Auto to ON. That will run the fan continuously. Let it like that for a couple weeks. It will raise the MRT slightly and your comfort levels will have a noticeable improvement.
Harvey
Ron Keagle
Again, we are not concerned about delivering heat to an individual. We are concerned with the manner in which a body looses it's excess heat. Air temperature plays a large part in the losses from the inside of our body through breathing. Put your finger to your nose, cool air going in, warm air coming out. MRT plays the largest role in the heat lost from the exterior of our body through radiation. We loose more heat through radiation than we do through convection and evaporation combined. Therefore if we take your example and move the air temp to 78°F and let the MRT drop, you will loose heat from your core slower and from your surface faster. For most people this would result in discomfort.
It is not an exact science. The level of an individuals activity, heart rate, ect.. will play a large role in the comfort they feel.
A radiant system is not magic. It is merely a comfort system that comes the closest to creating an environment that matches the bodies heat loss. If something better comes along I will be among the first to accept it.
Harvey
Response to Harvey Ramer
Harvey,
I understand your distinction between heat delivered to a person and heat loss from a person. But since the heat delivery determines the heat loss, I see them as indistinguishable for the purpose of this discussion.
I understand your point about this not being an exact science because of the difference in the heat perception by different individuals; and the differences in one individual, depending on activity, mood, metabolism, etc. So, I would stipulate that to make this as much of an exact science as possible, we should consider the effect of varying the radiant/conduction ratio on just one individual where all biological variables in that individual are constant.
So, regarding my other question, and based on what you have said in your reply to me, I would conclude the following:
The heat comfort producing effect of a btu of heat delivered to a person will vary according to the amount of that btu that is delivered by radiation as opposed to the amount delivered by air conduction.
If this is true, I regard it as being the critical point in differentiating both the performance and the economics of the two types of heating. If it is true, it means that a btu is not the same no matter whether delivered by radiation or conduction.
Ron Keagle
It appears that your understanding is correct.
Just for accuracies sake I would point out that the transfer of heat that occurs between a person and air is for the most part convection rather than conduction. That is, unless you are sweating, then you experience an evaporative (latent) cooling effect.
Harvey
Are we all made of mush?
I have thoroughly enjoyed reading the article and all the responses.
I am 68 years old and was born in Wales. We lived in a stone two story house. The ground floor had a stone floor (uninsulated) and the upper story had a wooden floor. There was no central heating system. On a winter morning you could see your breath. My parents would light the coal fire in the dining room to warm up the house. I assure you that No one walked around in bare feet! We all survived and thought we were fine, because some people could not afford coal for every day use.
I now live in a mini home heated by a mini-split heat pump, backed up by the original baseboard heaters. I set the heat pump at 72F and the baseboards at 65F. It is a wonderfully inexpensive heating system, even for Canada.
It is only recently that we have had heating systems and controls that would maintain +/- 1 F.
Have a nice day, everyone!
To Harvey Ramer
Harvey,
I did notice that you referred to the heat transfer to and from skin as being convection, which I regard as accurate enough. But, my reasoning for calling it conduction is that the actual transfer is conduction by the contact of skin with air. I see convection as the dynamic means of placing the air in contact with the material that it will conduct heat to or from. So I have always assumed it accurate to say that conduction is a necessary component of convection. Or, wherever there is convection, conduction is always a part of it. But conduction can also occur without convection being involved.
But, back to this conclusion that I mentioned based on what you have said:
“The heat comfort producing effect of a btu of heat delivered to a person will vary according to the amount of that btu that is delivered by radiation as opposed to the amount delivered by air conduction.”
If the comfort producing effect of a btu can vary according the thermal means of transfer that delivers it to a person, then so can the cost of producing the comfort vary according to the thermal means of transfer.
meaningful and lively discussion
To the discussion about a btu of heat comparison between that generated by hydronic radiant concrete floor and that generated by a properly designed and sized forced air system, I believe there absolutely is a difference and a significant one at that, and I'm not talking about all the intricacies of heat transfer from body to air, air to body, radiant to air and back,, etc..
The main thing that really matters is how one perceives their individual thermal comfort in their home at any given moment in (let's say for a 24 hr time period). With a properly sized forced air system there will be an air handler and compressor cycling every 30-60 minutes (this assumes a well insulated home); forced air blowing hot or warm air from a specifically placed register. Depending on where you happen to be at any given moment (sitting reading or dining, walking, sleeping, etc.) you will first feel the 'push' of colder air against you before the warm or hot air reaches you. There repetitive air handler 'effort' of mixing hot and cold air is intermittent but still constant during the 24 hr day. An interesting way of looking at this event is turning a blow dryer (like used for your hair) on and off every 30 minutes or so. On the other hand, with a well designed radiant floor system, the warmth JUST IS, everywhere, both vertically and horizontally, noiselessly, with NO blowing hot and cold air, no recirculation of stale indoor, or dusty air (has the air filter been changed lately?). Personally, if I have a choice, I prefer the latter.
The consequences of a btu of forced air heat is fundamentally different than a btu radiantly delivered warmth.
Response to Martin Holliday Comment # 74
hold on a minute Martin . It is not as easy as you say / I say to sum it up . Let's get right down to it and "Do The Math" . Apples to Apples cost analysis . Let's take into consideration that we are offering the option to NOT bring the attic and or basement / crawl space within " " conditioned space , this action costs money and does not come without it's complications , Don't forget the space that ductwork takes up and the labor and material required to get it out of sight . You cannot avoid the fact that a 3/4" pipe can carry or remove the same amount of energy as a 14" x 8" duct . very home has to have a source for domestic water , can you use that for hot air , I think not . I can use it however to heat the home you refer to . You mentioned pumps , let's explore that now . The circulators that I would require to heat your super tight house would consume on average 13.5 watts and they would not have to run 24/7 , how many watts does the smallest most efficient forced air equipment require ? I would venture that it is much more than 13.5 watts .
The industry has done so much work to include an inferior product that it infuriates me , all so we can be cheap on first cost . I could heat this house inexpensively and cool it also without ductwork as can several other that have commented , I am not special and neither are they unfortunately we are the exception and not the rule as you have stated is not very much different from forced air tradesmen .
I for one as well as others whom have dedicated a good chunk of our lives looking at all the built environment from a different perspective , "house as a system" would be more than happy to better the lives of many through discussion and cooperation . Maybe GBA would like to join in that constructive discussion and not sling mud at an industry that has so much to offer yet is suffering because of poor math skills by a self serving portion of the building community . Would you care to do the math with me Martin ?
Now that you have met the some guys who don't care what a manufacturers rep says to sell product are you interested in what we can offer you , because obviously we are so few that what we are doing has not been brought to your attention .
I am up for the challenge and willing to discuss
Cost comparison challenge and/or ROI?
Is it agreed that radiant delivery of thermal comfort is superior to a hair dryer form of thermal comfort delivery?
What about the proverbial ROI? Return on Investment. The two operative words here are RETURN and INVESTMENT.
INVESTMENT: money and time (for thinking things through) for installation.
RETURN:
Financial: short term (higher up front costs-NOT directly out of pocket because construction loan actually pays); higher monthly mortgage payment BUT monthly cash flow higher because utility operating costs are significantly lower (monthly, month after month, year after year); equity/resale value - this is pretty obvious especially looking forward to inflation and forever rising utility rates.
Comfort: immediate, 24/7/365, year after year
Health: immediate, 24/7/365, year after year
Hmph...seems like a no brainer
Apples-to-Apples Experiment
I agree that each person will perceive heating comfort differently, but we have to get around that variable factor in order to make apples-to-apples comparisons of the two different heat distribution systems.
I suggest taking a sample of 100 people, and subject each one to variations of the same thermal energy in varying ratios of the delivery of warm air transfer and radiant transfer. Then ask the test subjects to rate their feelings of comfort.
If it is found that a rise in radiant temperature with a corresponding drop in air temperature makes the average subject feel warmer, then reduce the total thermal energy until the average subject feels the same as before the change in total thermal energy. The difference in thermal energy delivered at the two different stages of the experiment would represent the cost savings for reducing air temperature and compensating by increasing radiant temperature.
Response to Harvey Ramer (Comment #76)
Harvey,
It seems to me that you are trying to convince the occupants of superinsulated homes with triple-glazed windows that they are not as comfortable as they think they are -- or perhaps not as comfortable as they should be. You seem to be including the occupants of Passivhaus buildings in your analysis.
All I can tell you is that your analysis does not correspond in any way to my experience. I have spent time in superinsulated homes with triple-glazed windows; these buildings are extremely comfortable and easy to heat. Any attempt to convince these homeowners that they are uncomfortable, or should be investing thousands of dollars in heating equipment to raise their comfort levels a notch, strikes me as counterproductive or even pathological.
How comfortable must Americans be to finally be satisfied? The tendency of Americans to be unsatisfiable was analyzed by David Foster Wallace in his classic book, A Supposedly Fun Thing I'll Never Do Again -- a book which will make you laugh out loud, by the way.
Response to Roger Williams (Comment #80)
Roger,
You wrote, "I am 68 years old and was born in Wales. We lived in a stone two story house. The ground floor had a stone floor (uninsulated) and the upper story had a wooden floor. There was no central heating system. On a winter morning you could see your breath. My parents would light the coal fire in the dining room to warm up the house. I assure you that no one walked around in bare feet! We all survived and thought we were fine, because some people could not afford coal for every day use."
Thanks so much for providing this perspective. My family lived in the Netherlands in the late 1950s, while my father was pursuing his doctorate. In those post-war years, Europe was still recovering from the second World War. My family lived in an uninsulated bungalow with a coal stove (on which my mother boiled diapers). My mother recalls that she kept the potatoes in a wooden box under the bed because it was the only place in the house where the potatoes wouldn't freeze.
I'm glad that you are now comfortable with your minisplit!
Response to Richard McGrath (Comment #83)
Richard,
You wrote, "The [HVAC] industry has done so much work to include an inferior product [forced-air heating systems] that it infuriates me , all so we can be cheap on first cost . I could heat this house inexpensively and cool it also without ductwork as can several other that have commented."
I agree that there are many problems with the way forced-air heating systems are installed in the U.S. The typical problems with ducts drive me crazy, and GBA has been trying to educate contractors on duct-related issues.
I sometimes conclude that the best solution to the problem of bad ductwork is to choose a heating system without any ducts. Solutions include ductless minisplits, gas-fired space heaters with through-the-wall ducting, electric-resistance heaters, and wood stoves. These solutions "cut the Gordian knot" of bad ductwork.
Of course, in-floor hydronic tubing is also a duct-free solution. But it is expensive, and it doesn't provide cooling (unless you also install a separate dehumidification system).
Response to Michael Ginsburg (Comment #84)
Michael,
You wrote, "Financial: ... higher monthly mortgage payment BUT monthly cash flow higher because utility operating costs are significantly lower (monthly, month after month, year after year); ... Comfort: immediate, 24/7/365, year after year; Health: immediate, 24/7/365, year after year."
These two claims -- that occupants of homes with in-floor hydronic tubing have lower energy bills and are healthier that occupants of homes with other types of heat distribution -- are unsupported by any data whatsoever. No study has ever substantiated either of these two claims.
Response to Ron Keagle (Comment #85)
Ron,
You proposed a research study: "If it is found that a rise in radiant temperature with a corresponding drop in air temperature makes the average subject feel warmer, then reduce the total thermal energy until the average subject feels the same as before the change in total thermal energy. The difference in thermal energy delivered at the two different stages of the experiment would represent the cost savings for reducing air temperature and compensating by increasing radiant temperature."
I love research, and would welcome any data coming out of your study. However, I'd like to point out:
1. You may find it difficult to get existing, on-the-market heating and cooling equipment to create the conditions you want to create in the study (low air temperatures with high mean radiant temperatures). This combination will either demand a house with a very leaky, poorly insulated envelope, or an air conditioner to cool the air while heat is being pumped through hydronic tubing. The results of the study might be technically interesting but irrelevant to HVAC decisions.
2. Your speculations imply that there are energy savings out there just waiting to be plucked from the branches, through the use of hydronic tubing. In fact, energy researchers have been looking at ways to save energy in homes for decades, and the methods that work are well understood. Switching from forced-air heat distribution to hydronic heat distribution, or switching from fin-tube baseboard to in-floor hydronic tubing, are not approaches that yield significant energy savings. This fact is well understood by energy researchers and weatherization researchers.
Response to Martin Holladay (comment # 90)
Martin,
I understand your point about needing a leaky house to replicate the conditions of my experiment. A surrounding surface of radiant emitters will inevitably heat all the air in the space to the temperature of the emitter surfaces. So it might indeed require chilling the air for my experiment to take place, and such chilled air would represent the effect of a leaky house, which we do not want in practice.
However, the point of my experiment would be merely to find the effects of changing the ratio of radiation/air conduction in heat delivered to humans. To find that effect, I would vary this ratio widely, even though its extremes would go far beyond what might be practical or worthwhile in an actual house being lived in.
My speculation about energy savings from shifting to predominate radiant have nothing to do with the hydronic tubing, fin tube radiation, or heated floor slabs per se. I agree that these things have been heavily researched and are well understood. However, the experiment I proposed focuses strictly on the effect of heating people with radiant transfer versus conductive transfer from heated air.
I don’t believe that is well understood at all, as you say, but I would welcome the revelation of studies and research that indicate otherwise. I certainly disagree that the information learned from the study I propose would be irrelevant to HVAC decisions, as you say. If it reveals a heretofore unrecognized greater potential for comfort, or an operating cost advantage, it would be highly relevant.
Aside from widely varying the conditions for the purpose of my experiment, here is the practical effect I would be inquiring about:
Even in a tight, superinsulated house, with a warm air heat distribution system, the wall surfaces are likely to be colder than the air temperature. So when conditions are considered to be comfortable, there will be heat conducted to the occupants by the warmed air, and heat lost from the occupants by radiant transfer to the walls.
I want to compare this condition to one where the walls are heated to the point where they match the air temperature as their emitting surfaces conduct heat to the air by conduction and disperse it throughout the space by convection.
Then I want to compare the relative perceived comfort of these two conditions, and discover whether the cost might vary between the two conditions at the same comfort level.
I also want to discover the maximum comfort level attainable with each of these two conditions, and whether one is greater than the other.
Michael
"Financial: short term (higher up front costs-NOT directly out of pocket because construction loan actually pays);"
I saw this argument first rolled out by the Passive House proponents in an effort to show that their more expensive construction costs really didn't count, and I don't think it holds much water.
When you increase the amount you borrow for a construction loan, that amount reduces the amount of credit available to you for other things. So for many people it may mean a smaller house or not including other features - and this occurs whether the increase in the loan has a payback in terms of reduced operating costs or not. Similarly, the simple analysis comparing the cost of carrying the loan being put against some reduced energy costs ignores that the increased credit you have drawn upon may well have had a better return used in another manner, either within the construction budget or by investing win a completely different area. Credit isn't free
Confused
I am reading the comments and am confused as to what the subject is. Is it a question as to radiant heats efficiency, comfort, cost or all of the above. Who am I to question what a customer has in mind that they would pay for comfort. As to the efficiency radiant is hands down the most efficient way to provide heating and now cooling comfort in the industry hands down. This comes with real, actual numbers not from some body guessing.
The idea that our feet may not feel the warm floors may be misleading. The bottom of your feet will always feel the warmth as compared to the top of your feet that will be losing heat more quickly. The floor should always be a few degrees warmer than the air around it. I think this is basic physics.
As far as radiant cooling. We have at our disposal several means of satisfying latent cooling such as conditioned dehumidification. Also using products such as Sunboard radiant panels with graphite coating just below the finished floor provides considerable quick response to the thermostat demands. This can also be used in walls and ceilings as has been mentioned. In fact in many commercial uses of chilled beam air conditioning it is still a radiant cooling scenario.
We must not forget that during the heating months from say November to March the hot water demands of a residence are almost free with the use of a boiler to provide both heat and hot water.
Again all of this is based on "proper" installation methods which in my experience in this neck of the woods has been lacking to a significant degree. Plain fact is hot water provides significantly more BTU's per size and heat transfer than heating or cooling air. It is quite and benign to the end user and much more even thus preventing the customer from noticing heat loss or gain from their skin.
Response to John Langan
John,
Q. "I am reading the comments and am confused as to what the subject is. Is it a question as to radiant heats efficiency, comfort, cost, or all of the above?"
A. This is an open forum for comments. All of the above topics have been commented on, and you are free to do so as well.
Q. "Who am I to question what a customer has in mind, that they would pay for comfort?"
A. If a customer wants a floor with in-floor hydronic tubing, it makes perfect sense to provide it for that customer.
Rsponse to Martin Holliday Comment # 88
Martin ,
Please correct me if I am wrong . Would a house as tight as the one you originally mentioned require mechanical ventilation ? If so , for very few additional dollars couldn't one employ a condensing dehumidifier that provides fresh air also ?
The point I have obviously not been successful in making is that under the watchful eye of one whom understands building as a system , thermal dynamics , physics and IEQ this does not have to cost so much as it has been demonstrated by individuals in the past whom do not design , allow their supplier to tell them what they require and do not understand nor care about house as a system , comfort , any of the things we concern ourselves with . You must do this comparison using a different metric other than the "this is how it has been done " theory . You must also take into account that while some successful contractors (financially)that are installing radiant at present really are not that successful (quality) , these are the men whose installed systems are being used as our control group . Would you not rather have a designer installer that along with knowing how to do it knows WHY he is doing what he is ?
My point being this , I could probably heat and cool this home using a small number of solar thermal panels , a small storage tank (highly insulated of course) and a minimum of tubing since our per square foot BTU requirement is so miniscule , source could be a very small air / water HP , condensing dehumidifier with fresh air capability and if you're concerned about HP performance on really cold days the water heater which is already there can be setup as backup for heat . Sounds to me like it does not have to be that almighty additionally expensive . Then again what the heck do I know , I'm just a hydronic designer / installer that is trying to insure that consumers are happy , healthy , and give less of their hard earned money to the utilities . Increasing our market share and educating the buying public is just an added benefit .
Still waiting for the design parameters to prove my theory (FACT) .
Response to Richard McGrath (Comment #95)
Richard,
Q. "Would a house as tight as the one you originally mentioned require mechanical ventilation?"
A. Yes.
Q. "If so, for very few additional dollars couldn't one employ a condensing dehumidifier that provides fresh air also?"
A. No. A whole-house dehumidifier costs thousands of dollars (installed).
Q. "I could probably heat and cool this home using a small number of solar thermal panels, a small storage tank (highly insulated of course) and a minimum of tubing."
A. Such a system is useful in some climates -- but not where I live, in northern New England -- and there are no locations in the U.S. where such a system will be cost-effective. It's really hard to beat one or two gas-fired space heaters, or one or two ductless minisplits, when it comes to cost-effective heating for a superinsulated house.
Response to M.Taylor- post 92
" I don't think it holds much water" A couple points to illustrate that "it" does in fact hold water.
It has been well established but not well known that a low HERS index (Home Energy Rating Score, a certified measure of a homes energy efficiency) does, in fact, result in a corresponding LOWER monthly utility expense. Because of this, one's qualifying mortgage amount proportionately increases so if you want you can have granite counter tops or one's monthly cash flow increase can be spent or invested anywhere YOU chose.
This expense evaluation process has been formalized with the appraisal institute with in the last year and EEMs (energy efficiency mortgages) have been available for many years. Furthermore, with the likelihood of congressional passage of the pending SAVE Act (Sensible Accounting to Value Energy) the mortgage industry as a whole, will then be required to make the PITI become PITIE(energy costs) when qualifying for a mortgage.
A HERS index number is similar to miles per gallon for a car but in reverse; meaning the lower the score the better with the 'ultimate' being 0. This means your monthly utility bill (based on a full year average) approaches 0 dollars.
Michael
"energy efficiency mortgages have been available for many years"
They must rank among the best kept secrets in the industry - and it certainly not the case here in Canada.
Even accepting their availability doesn't deal with the larger issue that by whatever method you have increased the amount you have borrowed and thereby precluded other borrowing for what may be equally useful efficiencies or investments.
It also sidesteps the issue as to whether the heating system you are borrowing for is the most efficient one or rather is simply more efficient that the current industry standard. If you can increase your mortgage to include radiant heat, why not do the same for a mini-split or other system instead?
Question for Martin
Richard wrote :
Q. "I could probably heat and cool this home using a small number of solar thermal panels, a small storage tank (highly insulated of course) and a minimum of tubing."
Martin responded :
A. Such a system is useful in some climates -- but not where I live, in northern New England -- and there are no locations in the U.S. where such a system will be cost-effective. It's really hard to beat one or two gas-fired space heaters, or one or two ductless minisplits, when it comes to cost-effective heating for a superinsulated house.
Questions for Martin :
1. Could you tell us what type , make or model gas fired space heaters you would recommend ? also what ductless mini split you would also recommend ?
I really am trying to grasp the energy efficiency benefit of these types of units above what a wet based system has to offer , please help me understand .
2. I still can't figure out what expensive is either Martin could you define expensive ? It is expensive to construct a passive house in almost every aspect to begin with , why would we stop and consider only price when we get to the systems that use what we ar attempting to save ?
I also am excited about the possibility of doing the apples to apples comparison of what your systems and mine cost in ACTUALITY.
Response to Richard McGrath (Comment #99)
Richard,
For a good example of a cost-effective approach to heating equipment, you might want to look at the homes built by R. Carter Scott in Massachusetts. Here's a link to an article: Just Two Minisplits Heat and Cool the Whole House.
Carter Scott pays his HVAC contractor less than $6,000 to install heating and cooling systems in his two-story homes, which range from 1,200 to 2,000 square feet.
The ductless minisplits that work best in cold climates are manufactured by Mitsubishi and Fujitsu.
Solar thermal systems for domestic hot water generally cost between $5,000 and $9,000 (installed) in New England, although do-it-yourselfers can, of course, do it for less. Such a system will supply about half the typical family's domestic hot water on a year-round basis, but no space heat.
The problem with trying to use an active solar thermal system for space heating in New England is that our region gets almost no sunlight in November and December, when space heating is generally needed. The situation tends to improve in the second week of February.
No sunlight
Martin ,
I am not from Mars and quite probably get the same amount of sunlight as you . Mr Scott seems to be concerned with nothing but cost . I thought we were both efficiency minded as opposed to bottom line minded , hell this guy thought cool air would rise and if his non profit contractor was worth his salt he would have pointed that out to Mr Scott . I would be very interested in how those heat pimps worked this past winter Not really since they are 2xs oversized and operate at roughly 60-70% below zero they were probably just right .
Natural gas versus propane . In my market nat gas costs 52 cents per therm , 100,000 BTU where as Propane if you are capable of taking bulk delivery costs 1.57 per gallon ( 91,800 BTU) , most people cannot though so let's use 4,29 per gallon . Don't forget that the propane must be delivered in a truck which usually consumes diesel fuel . I thought we were trying to save energy .
Let's not forget electric . So you ar gonna put panels on your roof to generate electric to be used in your home and put the rest into the grid and for 10 years the utility will pay you for what you provide them , how noble of them . Wait till you have to repair or replace them , you're on your own . While we are talking solar I have a question , how do those panels that are not quite yet harvesting the sun's energy above 40% working since a solar thermal panel that average 80% solar fraction will not work or is not efficient . Pumps you spoke of running constantly . The circs I utilize regularly could run 24/7 for 17.6 days on what those solar pv panels can produce in a day , how many watts , oh I'm sorry Kw do those heat pumps use .
Seems to me that Mr Scott has a problem with anyone but himself making a profit .
Real quality mechanical ventilation should not be an upgrade either Martin , we should be including it
in these houses .
I am still interested in your recommendation for a gas fired space heater .
Response to Richard
Richard,
Q. "I am not from Mars and quite probably get the same amount of sunlight as you."
A. OK. If you also live in northern Vermont, we're in the same boat, and neither of us will benefit from a solar thermal system in November or December. Other people live in Colorado, where insolation levels are much higher.
Q. "Mr. Scott seems to be concerned with nothing but cost."
A. Have you met him? Carter Scott is very smart, and he is a thoughtful builder who has considered energy issues and building science issues long and hard. I disagree with you about your assessment of Carter Scott.
Q. "I thought we were both efficiency-minded as opposed to bottom-line minded."
A. If heating loads are very low, it can be argued that the most efficient equipment (for example, a condensing furnace or a ground-source heat pump) might be so much more expensive than easier-to-install alternatives that the capital investment isn't worth it compared to lower efficiency options. However, if all you care about is efficiency, without regard to capital costs, you would clearly gravitate toward a condensing furnace or a ground-source heat pump.
GSHP
is the worst thing in the world . Tal about money down the tubes . Don't even get me started on COPs and funny math that do not include the source side pumping power consumption anymore . Advice , stay away from GSHP , even if someone lies to you by calling it geo thermal , it is not .
My opinion of Mr. Scott is this . An 8.50 per month charge for service and a meter to your location is just business . Now , don't get me wrong , the utility companies are not my favorite entity but they do have infrastructure to maintain and employees to pay for just sitting around many times waiting for the " I smell gas in my house " call . These things cost money . I would be more upset that rate payer money is being used to award Mr . Scott 8,000.00 per dwelling and more upset that as a builder I cannot qualify for the same incentive as a homeowner who undertook the same work .
My point has been throughout this discussion that hydronic solutions do not have to be that almighty expensive . Unfortunately the buying public and well intentioned folks like yourself have been looking to the wrong people and / or entities to assist you in your quest . You say radiant floors exposed to direct sunlight tend to overheat and you are correct but why can't we exploit that condition . It is my opinion that if we are making these homes this tight there certainly ought to be equipment capable of using only the energy required to hat that space at that moment based on conditions at that time . Still and I fear for a long time to come we will not count our money or budget these projects properly and begin to be frugal when it comes to the systems which in the beginning were what we were attempting to make smaller, more efficient or not even needed . All this work to oversize installed equipment by 2x's .
I assure you that there are systems that can be designed that can be competitively priced and meet the demands at a given time and temperature . I suggest you get a new rolodex and start identifying the people that can actually further your venture as opposed to those who really aren't that innovative .
The hydronics market could certainly use the boost and you could all certainly benefit form what we have to offer the near zero energy market . I would quote Joe L here but am afraid it would come across the wrong way , you know the title of the literary masterpiece I would refer to .
Just saying it is too expensive and it cannot be done just does not get it Martin , especially from one of your influence , you must inquire about what we have been diligently working on and how it can benefit all markets . Green building Advisor certainly accepts some hydronic companies advertising dollars , show a little love . Many of us have made it our business to learn what your segment has been working on to benefit all , will you do the same ?
Just a hint , STORAGE . From many different sources . The sun does shine in the summer in Vermont , does it not ?
Response to Richard McGrath
Richard,
Q. "Just a hint: STORAGE. From many different sources. The sun does shine in the summer in Vermont, does it not?"
A. There is absolutely no evidence to support the idea of cost-effective seasonal storage of heat collected during the summer for use in the winter. For more information on this idea, see Using Sand to Store Solar Energy.
Richard
"Green building Advisor certainly accepts some hydronic companies advertising dollars , show a little love"
What a cynical addition to the discussion.
disengenous responses
Seems many times your responses are very disingenuous. You cherry pick points to respond without addressing the meat of the matter from McGrath's comments and many others.
You've said you 'love research'. Spending a few moments in a home with radiant floor comfort is pretty thin research on your part.
Many of us have been ACTIVELY involved with researching, developing, prototyping, testing, monitoring, experimenting and experiencing active radiant comfort systems.
Have you? or, do you just talk with those who have been unsuccessful in their efforts and report these failed attempts as your researched facts?
You would do your readers or bloggers a greater service by engaging in a more pointed discussion of this topic.
Response to Michael Ginsburg
Michael,
Concerning questions of comfort: all of the statements I have made on this topic are consistent. Almost all occupants of homes with in-floor hydronic tubing report that these systems are very comfortable.
I try to keep up with relevant research papers on this topic. If you would like to cite research that undermines the conclusions I have shared, please provide the citations.
You wrote, "You would do your readers or bloggers a greater service by engaging in a more pointed discussion of this topic." I'm surprised at that! Many people in the hydronic community feel that my writing has already been too pointed.
Comfort versus green, I choose comfort
I will always remember my wife questioning why we would need to invest in a geothermal heating system and a separate boiler to heat the basement of our home. By the way we heat for $650.00/year in Minnesota.
Let me preface this, at the time we built in 1999, combination geothermal systems doing both forced air and radiant floor heating were not yet perfected by manufacturers. Many today are separate systems.
We were a young couple building our first home and wanted to save money. She was always questioning me why don't we do what most people do and put in a gas furnace with an AC unit. Long story short, I will always remember the words she uttered after being in our home for the first winter. She said, "I don't know how radiant floor heating works, but I know it when I feel it!"
I dare anyone to come over and tell her to change out our radiant floor heating system and stay with just the forced air geothermal system. She will NOT sacrifice her comfort or those of our children. Furthermore she, along with myself, have no problem having to pay for it regardless how people think if it as being green energy or not. Bottom line for our household is that comfort triumphs being green.
Radiant floor heating and effciency
I have read your article about Radiant floors and the long discussions on the blog, a lot of opinions and experiences with radiant floors.
I have built a few high-efficiency homes in Whistler BC, including one that tried to be net zero. Radiant floors are a luxury and do not work well to heat a home. We had to add duct heating after struggling through a winter heating season. Even-though all the homes are high efficiency houses and one has thermal mass walls (rammed earth). Air movement and heat distribution are critical for comfort, thus we used a 'air displacement ventilation' which helped circulate the warmed air to all parts of the house (very low speed air circulation).
In my experience as a 'home energy professional', radiant heating is expensive and not 'efficient' for the average home owner who wants to reduce energy bills. It works well in some homes with limitations in most. The home owner must be educated on what to expect and how to live with radiant floor heating.
Comfort
I keep coming back to Mark Etherton's definition of comfort as being a lack of awareness of your surroundings - a sort of neutral environment.
What strikes me is that this is very different from how we describe our pleasurable sensations outside. We go to the beach to experience the hot sun, enjoy a walk in the fall with the wind in our faces, a cold dip in a lake. It is the stimulus which makes us feel related and involved in our surroundings. And outside we think nothing of constantly altering our personal insulation to the varying changes in temperature.
One of the pleasures of the radiant heat source in my house, the wood stove, is it's stimulus, the way it waxes and wanes. I wonder whether the neutral model of comfort doesn't give up something - a certain engagement - in return for it's consistency.
Response to Malcolm Taylor
Malcolm,
Thanks for your comments, which are similar to those I wrote in Comment #39.
In that posting, I wrote, "You [Mark Eatherton] describe a comfortable person as someone who is ‘not aware of his surroundings. ... You are not hot, nor are you cold. You are not over-humidified nor are you under-humidified. ... Simply stated, you are not thinking about it.’ This person may be comfortable. It's also possible that this person is dead. In other words, some people don't mind feeling alive -- knowing when they are a little warm or a little cold is not a bad thing. When I go outdoors in perfect weather, I can assure you, I'm thinking about it."
Malcolm, fireplaces,
Malcolm, fireplaces, woodstoves are nice... listening to air move with a forced air system to me is the pits. I despise them. And AC... despise it. ceiling fans, love them. radiant floors, love them.
And yes... the outside... nature... the best. the mountains... the oceans... beaches.... surfing... skiing at 60 mph... hang gliding across Florida... no engines... just me and other gliders... and some red tail hawks... eye to eye at times! Had the talons of a hawk about two feet in front of my face one time when he thought I was in his thermal not our thermal.
AJ
Perhaps strangely, if I had to describe what for me is the archetypal Canadian sound it would probably be an almost completely still morning in a mountain valley where the only sound was the low rumble of a car's tires on a distant country highway.
comfort...forced air...radiant....
All this peripheral opining about 'what comfort is' ... pure and simple, comfort is relative. And, pure and simple the bottom line is how an individual prefers their thermal comfort when at home, sitting on the couch relaxing, watching TV, eating at the dining table or bar stool, sleeping in bed etc., etc., etc.. and how to achieve and maintain this condition.
As a design/builder general contractor (40 years+) I HAVE to presume that 'around 75F' is THE desired GOAL of any comfort system knowing full well that this mid 75F temp is always approximate because IT WILL VARY no matter how tight the home is, there are just too many variables, let alone people variables. The ability to generate and maintain this mid range temp is what it's all about, thermally speaking, that is.
When Mr. Eatherton says "...Simply stated, you are not thinking about it", he obviously means that the thermal comfort does NOT vary every 30 minutes or so when a forced air system goes on blowing hot or cold air in your face or personal space when you are sitting on your couch having a nice snooze for awhile! He's sleeping comfortably, not dead.
When Mr. Holladay says "...This person may be comfortable. It's also possible that this person is dead. In other words, some people don't mind feeling alive -- knowing when they are a little warm or a little cold is not a bad thing..."
Once again, Mr. Holladay, your 'musings of an energy nerd' is certainly anything but musing. It's insulting and does not foster intelligent dialogue about this topic.
A neutral environment means THE 75F TEMP JUST IS, all the time.....you NEVER have to experience RECIRCULATED HOT AND COLD BLOWING AIR IN YOUR FACE OR PERSON day or night. I cannot imagine anyone would prefer the latter.
Comment 109 radiant floor heating and efficiency
Perhaps you should re-read comment 108 about how effective radiant floor heating can be in cold climates such as Minnesota.
It seems your efforts at building high energy efficient homes and radiant comfort produced poor results, that's too bad. Whoever designed the thermal efficiency of the home's (full surround) shell and radiant comfort system made some big mistakes. The rammed earth for one up north is a BIG mistake; did you have any insulation on the outside of the rammed earth walls?, if not, than you sealed the fate of the energy efficiency of the home right there. And, the walls are only a third (if that much) of the thermal envelope. Did you insulate the floor? how 'bout air sealing of the home? what was its ACH?
Your experience as a 'home energy professional' apparently has been pretty limited and your failed efforts at effective radiant floor heating is not a valid benchmark from which to state "radiant floors are a luxury and do not work well to heat a home" . Even Mr. Holladay, in his limited experience, knows how well radiant floor heating can work IF designed and installed properly AND done so in a well insulated home.
Comparing thermal comfort (in a well built home) generated and maintained by a hydronic radiant floor system and that generated and maintained by a forced air system is pretty easy, actually. Would you prefer blowing hot and cold air creating varying micro climates or thermal comfort that JUST IS, ALL THE TIME, EVERYWHERE WITHOUT FORCED AIR.
Michael
A series of bellicose responses to anyone who doesn't share your views isn't furthering the discussion either. I came into this believing that radiant heat was certainly a good option to consider in terms of the quality of environment it provides. That belief being in part due to Martin's blog where he makes that point repeatedly . The questions that still go begging are at what price and what is their efficiency compared to other options.? I think it's fair to say, apart from generalities, the proponents have been coy or mute in answering those points. Why is that and why are you getting so mad?
FACTS
http://www.radiantandhydronics.com/articles/86660-beautiful-heat-sets-baselines-for-residential-radiant-heat-efficiency-in-canada
Richard
Thank you for the link. I do have a few reservations about the study. The first being that it is sponsored by an industry lobbying group as opposed to a university or independent source. The second, and perhaps you can correct me if I have misunderstood, but it appears to have used software to estimate the amount by which occupants can set back their thermostats, and extrapolates savings from that. This still doesn't address the initial cost of the system or its efficiency, nor does it deal with the very well insulated houses Martin's blog suggests radiant heat is unsuitable for.
Again thanks for providing some real meat which we can use as a starting point for an informed discussion.
Malcolm, instead of
Malcolm, instead of questioning others, get yourself in a home with radiant floor heat. Done. You will experience why it is liked. As to cost, add $4/sqft to the cost of a cheap cheap quicky air system.
AJ
With all respect that isn't a useful or practical suggestion.
Malcolm
I will comment one more time only because you seem genuinely interested .
While Martin's Title was about radiant floors I am speaking of radiant in general . More specifically radiant ceilings . In a home such as we are referring this is by far the most superior system you can get . I will explain and you can make your own conclusion .
First let us say that scientifically hot goes to cold and this type of system has been employed for years . Minimal tubing in the ceiling transmitting it's energy through drywall with an R Value of .4 does not require water temps much higher than 90* deliver the BTUs we need at design conditions . A very small storage tank in the location of mechanicals would suffice as storage , of course you could go anywhere you wanted with this but for now I'll keep it basic . All houses need a water heater , let's say this will have dual purposes . As for the water hater , that could be fitted to add heat to the storage tank also for those concerned with underperformance of an Air / Water HP .
Air to water heat pump , heat pump engages on call for replenishment of tank , tank supplies fluid to system tubing recognizing outdoor reset logic . This maximizes the heat pump efficiency . The thermostats are in fact humidistats that during summer will keep our cooling fluid for sensible load at roughly 3-5 * above dewpoint to prevent condensation . The only ductwork should be a minimally sized system to distribute fresh air and remove latent load (dehumidify).
Now take into account that the 2 to 3 pumps required for this are Delta T controlled meaning the fluid during either season will be moving the fluid at the exact rate of heat loss or gain optimizing the connected equipment . Did I mention that they will also use 22 watts or less when operating at
design and down to as little as 9 watts above design (winter) or below design (summer) . The ductwork considering the small amount of air it will ever move can be very small and probably installed within the conventional framing and inside the envelope without making the thermal envelope larger . No soffits , bulkheads or any other nonsense .
You are building a certain type of house for energy efficiency , you might as well be comfortable year round also . Maybe you could even steal some heat out of that floor that used to concern us and add it to the buffer / storage tank .
Not really that expensive and when you really start crunching the numbers probably right around the same unless a couple (2-3) thousand will break you . Later on when energy costs really rise all the way around solar thermal can be added .
Do some research , do some math . There really is not anything crazy about this , just a true definition of efficiency and comfort . By the way if a more efficient , more environmentally friendly system without compromises in comfort after considering all the math and utility bill differences is a break even why in the world wouldn't you do it .
Malcolm 116
"A series of bellicose responses to anyone who doesn't share your views isn't furthering the discussion either. The questions that still go begging are at what price and what is their efficiency compared to other options? I think it's fair to say, apart from generalities, the proponents have been coy or mute in answering those points. Why is that and why are you getting so mad?"
I apologize for the seeming 'bellicosity' of my responses, not intended to be that. What's bothersome is when radiant comfort systems (in any climate) are 'tried' and the results are unsatisfactory and needing forced air mitigation (and the costs associated thereto), they then categorically claim radiant comfort systems are a poor choice for cost, efficiency and comfort.
Most people, yourself included I presume, have never "visited", lived in even for a few days (weekend) any successful radiant comfort system. I guess this is not very likely, possible or desired by those who are curious or like to opine. Oh, and being able to 'compare' two system's (radiant & forced air) operation in real time, apples to apples so to speak, not likely - who is going to build two “identical houses” with one incorporating radiant and the other incorporating forced air??? This is unfortunate but is the reality. Therefore, all in this group (most everybody) have to rely on second hand information, data, technical reports and opinions of others from all sources - radiant and forced air opined examples.
My "views" are like others who have personally experienced successful radiant comfort. BUT, unlike these others, my "views" are based on first-hand knowledge and experience in conjunction with DOE Building America Program research engineers testing and monitoring with embedded sensors in, on and below the concrete floor, and elsewhere for real time data monitoring temperature, thermal comfort, humidity mitigation and ERV whole house ventilation. Construction was completed in late spring, 2011 with move in and testing protocols occurring for the next 2-3 years.
Moreover, and I can’t be 100% sure, but I think nowhere else has there been created a high performance thermal enveloped prototype new home that has BOTH a whole house radiant floor comfort system AND a whole house forced air comfort system to research. These two systems were tested independently and togethe, monitored, experimented with and (live in) experienced for almost three years now. The radiant system has three independent thermostat controlled zones, one for the main living area and one for each bedroom wing (split bedroom floor plan, single story). The ability to test so many combinations of thermal performance and electricity usage and humidity-dehumidity performance with set point thermostats and setback thermostat settings... a wealth of REAL TIME information (objective and subjective) has been gleaned. All of these reports, stories, presentations, and abstracts will be chronicled soon at our website. Plus, this summer at the annual ASHRAE conference and the biennial ACEEE conference the most recent evaluation and assessment abstracts will be presented.
No offence intended, but the opinions and experience of Mr. Holladay’s are antiquated and outdated. Sort of like musing about picture tube TVs when high def’ flat screen LED TVs have fully replaced the ‘old order’; smart phones compared to analogue phones? Which would you prefer moving forward into the future?
Michael
Well both sides have had a chance to make their case repeatedly, and I guess it is up to each of us to decide what we think. I look forward to the results of your research being available soon as I haven't been able to form any judgements one way or another on the two questions I have asked based on your responses so far.
Terrific discussion.
Not to be flip, but isn't a solution to build a less-insulated house? Having lived in a leaky old house with hydronic radiant floor heat for 20+ years, I can't really imagine not having it in a new build. (Of course I am assuming the boiler is PV powered.)
Dackdotcom,
Indeed. Compensating for architectural features, like glass curtain walls, by using more energy is a longstanding tradition within the profession. However if energy use and efficiency isn't a priority, GBA is probably not the right forum for the discussion. Isn't that sort of what the whole site is about?
Malcolm:
"Isn't that sort of what the whole site is about?"
Kind of? Just looking at the GBA home page and there are many other topics besides energy use and efficiency.
But it's besides the point. What I am getting at is, with a PV array powering my radiant heat boiler (and everything else), does it really matter if my slab is merely code minimum? Or if I insist on double-hungs? And also a fireplace?
I'm sincerely curious. On a recent BS and Beer MH himself said, "The amazing thing about an all-electric society, with an all-renewable electricity grid is, it's OK to waste energy. It doesn't matter how much you use. You don't have to be energy efficient anymore. When we reach the promised land, you know the golden arches and the rainbows and the unicorns and the birds are singing, who cares about saving energy?!"
https://youtu.be/7iriloYsSC0?t=2621
ddc,
That's an interesting perspective, and I hope it ends up being true. Some people are predicting an era of energy abundance that will make consumption a lot less important. It would be nice to be able to be a lot less hair-shirted about these sorts of decisions.
My predictive powers are laughably poor - and I seem to be naturally pessimistic, so I'm hedging my bets by planning on a certain level of efficiency being a good thing in the houses I do.
Dack,
Let's see -- I'm not sure how many people have their tongues in their cheeks right now.
Q. "Did Martin advise GBA readers that it's OK to waste energy?"
A. No. I kind of thought the reference to unicorns was a giveaway, but irony can be hard to detect sometimes. For the record, it's not OK to waste energy.
Q. "Can I heat my house with a PV-powered boiler?"
A. No. I've never heard of a PV-powered boiler. I guess that would be an electric-resistance boiler (ouch!) connected to a PV array. No one ever does that, because when the sun shines, a well-built house doesn't need any space heat. Here in Vermont, we mostly need space heat on cloudy winter days, and at night during the winter, when a PV array is worthless. And if you want to have a grid-powered electric-resistance boiler in your house, and a PV array in your yard for show, you can do that -- but the electricity bills will kill you. (I say "for show" because the PV array won't really be heating your boiler water -- most of its energy production will occur from April to October.)
Get a ductless minisplit instead.
Actually, there's no need for reducing the insulation. If you want to have the feeling of warm floors underfoot, without overheating the room, you can simply run a ducted air-conditioning system while also running the floor heat. You can use a temperature sensor in the floor to maintain a constant floor temperature, while using a thermostat with the air conditioning to set the room temperature.
I am not at all sincere about that suggestion, but in fact, I did hear of someone who did exactly that. I hope it was an apocryphal story.
Getting to abundant renewable energy seems increasingly within reach, but abundant renewable energy on winter nights in cold climates will be the last piece of that puzzle to fall into place, so if you are planning a building that's going to be completed within the next 40 years, it still makes sense to minimize winter energy consumption.
People used to think nuclear would be too cheap to meter. Same for renewables? I'd be skeptical given the immense capital investment and tech hurdles ahead of us in an uncertain political/economic climate.
From my laymen's seat, it seems we are still quite far from cracking the 'power generated intermittently but consumed when and how you want' nut. We're going to have to a) invest a lot of time and money on storage solutions and grid upgrades (which come with their own environmental costs), and/or b) adapt our lifestyles in a demand response fashion to the generation. Well insulated structures can be a form of storage and demand response both, so I think they are a smart bet more often than not. Of course to really get into it, we need to look at present costs (monetary and environmental) of the build vs future avoided costs-- hard to do. But if the present environmental costs are reduced by utilizing low embodied carbon methods, the calculation looks better.
And even if we are able to produce cheap 'surplus' power via renewables, we will find ways to use it, and therefore charge something for it. Or if we don't use it, we will have reduced the capacity factor of renewables and hence the capital cost recovery period (may or may not matter...?). Smart people have written about 'overbuilding' renewable base capacity and then just accepting significant curtailment, but that not a free proposition in a world where building infrastructure is politically, economically, and environmentally challenging. And until we internalize environmental externalities, our economics may be driven by the wrong equation.
All power generation that I am aware of exacts an environmental toll. By certain metrics, I imagine that the environmental costs of a vast renewable infrastructure will be greater than our existing fossil fuel infrastructure. BUT in significant other ways, the costs will be much less (one hopes). Trade offs. Worth making but not free.
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