Air conditioner efficiency ratings are designed to give buyers a good sense of system efficiency, similar to the way a miles-per-gallon rating measures fuel efficiency of cars. It’s good to get familiar with the two different rating systems so you’ll have a better idea of what to expect when considering a new cooling system.
Seasonal Energy Efficiency Ratio (SEER)
SEER is the cooling output during a typical cooling-season divided by the total electric energy used during the same period. A higher SEER rating is more efficient, meaning more savings on your electric bills over time. Since 2006, federal regulations require a minimum SEER rating of 13 for new air conditioners, but an older AC might be lower (units tend to decrease in efficiency over time). ENERGY STAR qualified central air conditioners have a SEER of at least 14.5, and units with this rating are often sufficient for the Northwest. Window units are less efficient so their SEERs maximize around around 10. Some mini-split (ductless) air conditioners are available with SEER ratings up to 33. Units with higher SEER cost more initially, but the savings over time may justify the higher upfront cost.
Energy Efficiency Ratio (EER)
EER, an older rating system, is a more technical way to rate an air conditioner’s efficiency, and is most often used by HVAC installers. It assumes a constant outside temperature of 95 degrees and a constant inside temperature of 80 degrees, with 50% humidity. EER does not take into account seasonal temperature changes.
Which rating system to use?
Both rating systems are based on assumptions, not actual operation in your home, so they have limitations. As a homeowner, you’ll probably find SEER more useful. It’s highly visible, included on federally mandated Energy Guide labels, whereas EER can be harder to find in product literature. Regardless of which rating system, it’s best to work with a quality contractor. Proper system sizing and correct installation are always the most important factors in the operating efficiency of your air conditioner.