ABOUT CENTRAL AIR CONDITIONING

Cooler, drier air and better energy performance

Air conditioners are significantly more efficient than they were in the 1970s and are now capable of producing the same amount of cooling with as much as 50% less energy, the government’s energy office says.

Watch the numbers. An air conditioner’s seasonal energy efficiency ratio (SEER) is key. That’s the total cooling capacity (in Btu) compared with total electrical input (in watt-hours) over the course of a cooling season.

The higher the SEER, the higher the energy efficiency. Minimum federal standards were increased in 2006 to SEER 13. Minimum SEER for an Energy Star rating is 14, but units with ratings of over 20 are available.

Get the right size. Output is measured by the ton, equal to 12,000 Btu/h. Residential systems are typically sized between 1 and 5 tons.

Some HVAC contractors oversize air-conditioning equipment just to make sure the house stays cool. But calculating the cooling load and buying the right capacity lowers purchase and operating costs.

Help the ozone layer. Chlorofluorocarbons, or CFCs, were widely used as a refrigerant until scientists discovered how much damage the chemicals did to the Earth’s ozone layer. They have been replaced by hydrochlorofluorocarbons (HCFCs) like R-22, which have substantially less ozone-damaging potential.

These, too, are gradually being phased out in favor of refrigerants that have no ozone-damaging potential, such as R-410a, which can be specified in some AC equipment.

More information. For an in-depth technical introduction to the nuts and bolts of air conditioners, see Air Conditioner Basics.