Window Air Conditioner also known as a room air conditioner, an appliance that cools a single room rather than an entire home or business. If they provide cooling only where they're needed, window air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.

Smaller window air conditioners – those drawing less than 7.5 amps of electricity – can be plugged into any 15- or 20-amp, 115-volt household circuit that is not shared with any other major appliances. Larger room air conditioners (those drawing more than 7.5 amps) need their own dedicated 115-volt circuit. The largest models require a dedicated 230-volt circuit.

Energy efficiency of window air conditioners

A window air conditioner's efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units per hour) to the power input (in watts). The higher the EER rating, the more efficient the air conditioner. National appliance standards require room air conditioners built after Jan. 1, 1990, to have an energy efficiency ratio (EER) of 8.0 or greater.

The Association of Home Appliance Manufacturers reports that the average EER of window air conditioners rose 47% from 1972 to 1991. If you own a 1970's-vintage room air conditioner with an EER of 5 and you replace it with a new one with an EER of 10, you will cut your air conditioning energy costs in half.