If you determine energy efficiency based only on the EER (Energy Efficiency Rating) numbers, window air conditioners score lower on average than a split system. Older window units, or recently purchased less-expensive ones, have an EER of about 9. More efficient (and more expensive) ones hover around a 12 EER, and the newer inverter-type window units are up at 15. The low EER of many window units is due to the fact that there is no minimum EER (or similar SEER) required by the government, and lower efficiency units are cheaper to produce.

    New split system air conditioners, on the other hand, are mandated to be minimum 14, with some models rated at over 20. To give you an idea of the difference: a 20 rating uses half as much electricity as a 10 for the same amount of cooling. Most window air conditioners are also less efficient at dehumidification—an important factor for indoor comfort—than a split system. 

Do Window Air Conditioners Use Too Much Electricity?

Most window air conditioners use about 1/3 more electricity per BTU of cooling than an average split system. But if you consider other factors, window units gain ground and may even be more cost efficient in some situations:

•• Window air conditioners can serve just one room. If you have a sun room that is only cooled occasionally, a window unit means the central HVAC does not have serve it year-round, or contend with the air leakage and back-pressure on the ducts from a closed vent when not in use. And a single person or couple that just uses one bedroom can choose to cool only that room overnight.

•• Good for locales that only need cooling briefly in the summer, like the Pacific Northwest, and can be removed at end of season. 

•• No ducts, so no “duct loss.” Even brand-new and well-sealed ducts will warm the air several degrees in transit to rooms distant from the air handler. Older, leaky ducts even more.  

    Ductless mini-split air conditioners share all of these advantages and are much more energy efficient. They are also whisper quiet, a big plus compared twindow units. But mini-splits are way more expensive, and difficult to install for the average homeowner. Low cost and easy installation are the two big advantages that make window air conditioners always popular. 

    Also, see our articles What are the most common problems with wall/window air conditioners? and Frequently Asked Questions (FAQ) about Window Air Conditioners

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.