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.

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.

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.