A Few Basic Terms

To help get the most from this booklet, you'll need to understand a few basic terms.

A British thermal unit (Btu) is a standard measure of heat energy. One Btu is the amount of heat energy required to raise the temperature of a pound of water by one degree Fahrenheit. Its metric thermal equivalent is 252 calories per hour. As a unit of power, one Btu/h equals 0.2929 watts (W). Manufacturers classify the size, or capacity, of an air-conditioning unit in terms of Btu/h.

Cooling capacity, measured in British thermal units per hour (Btu/h), indicates the quantity of heat a room air conditioner can remove in one hour.

Cooling load, also expressed in Btu/h, refers to the maximum amount of heat that can build up in a space without a cooling system.

A watt (W) is the standard unit of power; one kilowatt (kW) equals 1000 watts. You purchase electricity from your utility by the kilowatt hour (kWh), equivalent to the amount of power required to operate one 100-W light bulb for 10 hours. To estimate how much electricity an appliance uses, multiply the wattage of the machine by the number of hours it will run.

Energy efficiency ratio (EER) is a comparative measure of how much cooling an air conditioner provides for each unit of electrical energy that it consumes under standard operating conditions. A unit's EER is calculated by dividing its cooling capacity by its electrical power input at a specific temperature. In general, the higher the EER, the more efficient the unit.