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The cooling capacity of a window air conditioner is measured in British Thermal Units (BTUs).Window air conditioners remove humidity and heat from the air while cooling the room. Less energy efficient than central air conditioners, window or room air conditioners cost less upfront and have fewer operating costs. Enjoy the convenience of a window air conditioner for cooling small spaces or a few rooms. Sizing

Correctly size the air conditioner to prevent the unit from cycling off and on. Too large of a unit will leave too much moisture in the air, a result of the room cooling too quickly to remove the humidity from the air. The average British Thermal Unit (BTU) range for window air conditioners is between 5,500 to 14,000 BTUs per hour. Calculate 20 BTUs per square foot of living space for efficient cooling. For sunny or dark rooms, decrease or increase necessary BTUs by 10 percent. For kitchen window units, increase the number of BTUs needed by 4,000 BTUs per hour.

The energy efficiency ratio (EER) of a window air conditioner is based on the BTUs per hour relative to the power (wattage) per hour. The higher the EER rating is, the more efficient the window unit is. The U.S. Department of Energy recommends purchasing a window air conditioner with EER ratings of 10.0 or above.

Install your window air conditioner with a helper's assistance. Raise the lower window pane, and slide the air conditioner into place. Level the air conditioner so it doesn't tilt forward into the room. Some air conditioners are designed to tilt slightly backwards so that water from condensation can drain outside. Slide the window extensions into place, and seal the unit with weatherstripping. Popular Mechanics suggests using plywood to create extensions for odd-fitting windows.

Most window air conditioners require between 115 to 230 volts of power. The average household receptacle accommodates 115 volts of power. Large room air conditioners may require a special 230-volt circuit for safe operation.

Place window units in a shady area on the north or east side of your home. Direct sunlight can decrease the units' efficiency by 10 percent. Locate lamps or other appliances that give off heat away from your air conditioner's thermostat to prevent unnecessary cycling on and off. Lower the air conditioner's fan speed on humid days to slow air movement, thereby removing more humidity from the room. On non-humid days, take advantage of ceiling fans to circulate the cooled air.