The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio (SEER) which is defined by the Air Conditioning, Heating and Refrigeration Institute

Air Conditioning, Heating and Refrigeration Institute

The Air Conditioning, Heating and Refrigeration Institute , formed by a merger of the American Refrigerant Institute and the Gas Appliance Manufacturers Association , is a North American trade association of manufacturers of air conditioning, heating, and commercial refrigeration equipment...

 in its standard ARI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment.

The SEER rating of a unit is the cooling output in Btu (British thermal unit) during a typical cooling-season divided by the total electric energy input in watt-hours

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

 during the same period.