This is the final post in a four-part series covering the topic of data logging in terms of Home Applications, Products and Performance, Types of Monitoring, and Indoor Air Quality.

Expensive, research-grade instruments have been available to measure pollutants in indoor air for decades, but only in the last few years have Foobot, Awair, and similar low-cost, consumer-grade devices made indoor air quality (IAQ) monitoring practical for home use. Various low-cost sensors are wired into these devices and their proprietary software displays some version of what they’re reading. Compared to the other loggers I’ve discussed in this series, the accuracy of this group of devices is worse, but they are tools for learning about things we weren’t able to practically measure at all in the past.

Carbon dioxide

I’ve found carbon dioxide (CO2) to be the most helpful thing to measure. Obviously, when we breathe, we emit CO2. From the conversations I’ve had with IAQ researchers, CO2 is not considered a dangerous pollutant (though if you search around, you’ll find studies about mild cognitive impairment measured in people in rooms with high CO2). However, CO2 levels do tell us how well our ventilation system is working; if CO2 is building up, it means our exhalations are not being wafted away by air movement.

In my own house, I was surprised how bad the air was in my kid’s bedroom. I thought our leaky old house would have lots of airflow, but it turned out our child was breathing 2200ppm of CO2, and who knows what else was trapped in there. (There is some kind of “Total VOC” and particulate sensor on the Awair v1 I was using, but it did not generate useful information. I could tell when someone was vacuuming but other than that not much we did or didn’t do made the readings change.)

I started running the furnace fan 10 minutes per hour to mix up the air in all the rooms at night, and then watching the Awair to see if this was keeping CO2 below1000ppm—often considered a reasonably good level. (Again, search around for more on CO2 levels if you would like to learn how much is too much). It proved a good solution.

Particulates

Small particulate pollution is one of the best-studied pollutants in terms of health effects. Particulates below 2.5microns in size (called PM2.5) have been shown over and over to cause cardiovascular, lung, and other organ damage, and even to change our microbiome and to be associated with birth defects. Unfortunately, PM2.5 is difficult to accurately measure with low-cost instruments. The Lawrence Berkeley National Laboratory published a study of several brands of consumer-grade IAQ devices and none of the multi-sensor devices under $500 were great on particulates. Dylos makes a sensor that costs $550 and does give pretty accurate readings. For an example of what can be done with PM2.5 data, check out the ROCIS program run by Lynda Wiggington and Rhett Major. Their goal was to reduce particulate exposure among residents of western Pennsylvania. Using dozens of Dylos meters they recorded particulates before making any changes to houses. Then they measured again following multiple interventions, such as closing windows at night, adding box fans with high-MERV furnace filters, and improving HVAC systems and kitchen range venting. Having the baseline PM2.5 data led to improved IAQ.

VOCs

Volatile organic compounds (VOCs) are a group of usually smelly chemicals that are ubiquitous in our industrialized society. Indoors, they come from the off-gassing of furnishings, clothes, and rugs, and from personal care products, cosmetics, and cleaning solutions. The sensors in low-cost IAQ devices are triggered by a wide range of materials, which is both good and bad. On the plus side, it’s pretty easy to see when ventilation is inadequate to remove these pollutants. But since the sensors react to so many things, it’s not easy to understand what the problem is at any given time.

Radon

I know of at least one brand of IAQ monitor with a radon detector: Airthings Wave Plus. Radon should be controlled to the greatest extent possible. Ventilation usually helps by diluting radon with fresh outside air. With a monitor you can see whether a given level of ventilation is getting the job done. In some houses, pressure in the basement vs. pressure in upper levels can drive higher or lower radon infiltration. Using a monitor to follow radon levels can help achieve better control.

Monitoring IAQ is important for occupant health—and to ensure ventilation systems are operating optimally. As with all sensors, some are better than others, but I imagine devices will improve and costs will come down, given the newfound attention being given to the subject of IAQ.

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Doug Horgan is vice president of Best Practices at BOWA in Washington, D.C. Photo by Peter Yost.