Image 1 of 2 A window-mounted air conditioner could save you money. Homes that use window-mounted air conditioners use less energy for cooling than homes with central air conditioning. Window-mounted air conditioners (also called room air conditioners) aren’t particularly efficient; the best available models have an EEREnergy-efficiency rating or energy-efficiency ratio. As most commonly used, EER is the operating efficiency of a room air conditioner, measured in Btus of cooling output divided by the power consumption in watt-hours; the higher the EER, the greater the efficiency. of about 10 or 11. Central air conditioners (also called whole-house air conditioners or split-system air conditioners) are significantly more efficient; it’s possible to buy one with an EER of 14 or even 15. So if you care about energy efficiency, you should use a central air conditioner, not a window air conditioner — right? According to the American Council for an Energy-Efficient Economy, the electricity used for home air conditioning represents almost 5% of all the electricity produced in the U.S.

So if you are going to air condition your house, it would appear to make sense to buy the most efficient unit you can find. There are two metrics used to rate the efficiency of central air conditioners: the Energy Efficiency Ratio (EER) and the Seasonal Energy Efficiency RatioSeasonal Energy Efficiency Ratio (SEER) is the total cooling output (in BTU) of an air conditioner or heat pump during its normal annual usage period divided by its total energy input (in Watt-hours) during the same period. The units of SEER are Btu/W·h. SEER measures how efficiently a residential central cooling system operates over an entire cooling season. The relationship between SEER and EER depends on location, because equipment performance varies with climate factors like air temperature and humidity. (SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit.

For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive.The unit for both metrics is BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. GBA Encyclopedia: Cooling Options Using Ceiling Fans To Keep Cool Without AC EER is the cooling capacity of the appliance (in Btu/h) at an outdoor temperature of 95°F divided by the current draw of the appliance in watts. SEERSeasonal Energy Efficiency Ratio (SEER) is the total cooling output (in BTU) of an air conditioner or heat pump during its normal annual usage period divided by its total energy input (in Watt-hours) during the same period. is the total cooling output (in Btu) over the cooling season divided by the total electrical energy input (in watt-hours) over the cooling season. For typical residential air conditioners, EER equals about 0.875 SEER;

however, this ratio varies somewhat for different air conditioner models. Unlike central air conditioners — which are rated by both EER and SEER — room air conditioners (window units) are rated only by EER. Room air conditioners that use at least 10% less energy than the federal standard are eligible for an Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; ac unit replaceapplies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. thru the wall heat and cooling unitsWhen shopping for a room air conditioner, look for an Energy Star unit with an EER of 10.7 or more.types of window air conditioning units

The idea behind the SEER rating is to allow consumers to compare the seasonal efficiency (rather than the peak efficiency) of split-system air conditioners. If you are in the market for a new central air conditioner, look for an Energy Star unit with a SEER of at least 14.5 and an EER of at least 12. Some critics have noted that air conditioner manufacturers design equipment to achieve a high score on the laboratory SEER test, even when some of the engineering solutions used to achieve high test scores result in poor performance or efficiency in the field. For more information on perceived flaws in the SEER standard and SEER testing protocols, see SEER Ratings Challenged. John Proctor, the president of Proctor Engineering Group in San Rafael, California, has performed useful research into possible flaws in the SEER rating method. Proctor (with co-author Gabriel Cohn) has publshed a paper on the topic: Two-Stage High Efficiency Air Conditioners: Laboratory Ratings vs. Residential Installation Performance.

Proctor and Cohn wrote, “The increased installation of high Seasonal Energy Efficiency Ratio (SEER) air conditioners along with utility program rebates for these units prompted a study of the measured performance of these systems. This project assessed the performance of these systems in the climate zones found in the mid-Atlantic region of the U.S. ... The data were analyzed to assess the relationship between laboratory testing and real world performance. This study found causes for concern including: actual seasonal energy efficiency ratios between 59% and 84% of the rated SEERs, constant fan operation substantially degrading seasonal efficiencies and reducing dehumidification, latent loads that exceed Manual J estimates, and sensible loads substantially lower than Manual J estimates.” According to some experts, problems with the SEER rating system may make EER a more useful metric for comparing the efficiency of central air conditioners. Even though central air conditioners are more efficient than window-mounted air conditioners, homes equipped with window-mounted air conditioners use less energy for cooling than homes with central air conditioning.

For some readers, this fact will be unsurprising. After all, homes with central air conditioning usually maintain lower temperatures in more rooms than homes with window-mounted air conditioners. Other readers — including those who assume that equipment efficiency is the most important factor in energy use — may be surprised to learn that homes with window-mounted air conditioners are energy misers. For those interested in the data behind this question, I recommend a blog by fellow energy nerd Tim Grejtak, “The Fascinating World of Air Conditioner Efficiency.” According to Grejtak’s analysis, “Window ACs use less energy on a per cooling degree day and per square footage basis by a factor of 1.75.” So why do homes with window-mounted air conditioners use less energy for cooling? There are several reasons: There are several valuable lessons arising from this analysis: I’ll end with a gentle reminder: the correct abbreviation for “air conditioner” is AC (or A.C.).