Air Conditioner Power Requirements

Btu

• Air-conditioning power is typically expressed in British thermal unit (Btu), which is the amount of energy needed to raise the temperature of 1 pound of water by one degree Fahrenheit at normal atmospheric pressure. One kilowatt of electricity produces 3,412 Btu per hour, and a cubic foot of natural gas makes 1,027 Btu. The capacity of a small room air-conditioner might be 8,000 Btu. A large central air-conditioning unit, which can cool all the living spaces in a home, might have an 18,000 Btu capacity. Btu normally is listed on the energy labels of wall or room air conditioners. For central air-conditioning systems, one ton equals 12,000 Btu.

SEER

• Another important factor in judging air-conditioner power requirements is Seasonal Energy Efficiency Rating (SEER). It describes the amount of cooling an air conditioner produces for each watt of electricity it consumes. An air conditioner with a SEER of 10 is inefficient. A SEER of 11 to 14 means the unit has medium efficiency, and a SEER above 14 means the appliance has high efficiency. As of 2006, the U.S. government set the minimum SEER for central air conditioning at 13. If two air conditioners have the same Btu capacity and all other factors are equal, then the air conditioner with the higher SEER cools more efficiently and with less energy than the other unit.

Calculations

• A room air conditioners with 5,000 to 6,000 Btu will cool 100 to 300 square feet. A unit with 7,000 to 8,200 Btu will cool 250 to 400 square feet, and one with 9,800 to 12,500 Btu will cool 350 to 650 square feet.

  The best way to calculate power requirements for central air conditioners is to contact an air-conditioning contractor who uses the industry-standard calculation found in Manual J, “Residential Load Calculation,” published by the Air Conditioning Contractors of America. It takes into account factors such as the climate; the house's design, location and solar orientation; insulation; number of inhabitants; and the number and types of doors and windows.

Power

• Homeowners can maintain the power output of an air conditioner over its lifetime as well as improve energy use by performing a few simple tasks. Changing the air filter at least once each month during summer allows air to flow unimpeded by dirt or dust particles. Installing a programmable thermostat can automatically adjust the cooling rate according to when the home is used. Sealing air ducts can prevent cooled air from leaking and wasting energy to cool warm air unsealed ducts let inside. Also, a once-a-year tuneup, preferably before summer, can improve the air conditioner's energy efficiency.