This is a number assigned to every air conditioning unit based on how efficiently an AC unit uses up energy. This number is arrived at by taking the unit's BTU/hr divided by its electrical input in watts. The higher this number is, the more efficient the air conditioning unit is (and the more money it wills save you in the long run on your energy bill). Smaller units can have an EER up to about 11 while the most efficient larger model AC's can have an EER rating of up to 13. For example, an AC unit with an EER rating of 10 should use up to 20% less energy than a similar unit with an EER rating of 8.

The rating under which specified appliances or other electrical equipment convert energy sources into useful energy. It measures of overall efficiency for the appliance. For example, for water heaters, it is based on three factors: 1) the recovery efficiency, or how efficiently the heat from the energy source is transferred to the water; 2) standby losses, or the percentage of heat lost per hour from the stored water compared to the content of the water: and 3) cycling losses. For dishwashers, it measures the number of cycles per kWh of input power. For clothes washers, it measures the cubic foot capacity per kWh of input power per cycle. For clothes dryers, it measures the number of kilograms of clothes dried per kWh of power consumed.

A measure of how efficiently an appliance uses energy. Determined by dividing the Btu per hour output by the number of watts used. A higher EER means greater efficiency.