Coefficient of performance
COP
The coefficient of performance (COP) is the heat a heat pump delivers divided by the electricity it uses, measured at one set of conditions; electric resistance heat has a COP of 1.
COP compares heat out with energy in, both in the same units. A COP of 3 means three units of heat for each unit of electricity. A heat pump can exceed 1 because it moves heat from the outdoor air rather than making it. A resistance heater turns each unit of electricity into one unit of heat, a COP of 1.
A COP describes one operating point: one outdoor temperature, one indoor temperature, one compressor speed. It falls as the outdoor air gets colder, which is why cold-climate ratings quote it at 5 °F (−15 °C). ENERGY STAR’s Cold Climate designation requires at least 1.75 there. Units built for the DOE Cold Climate Heat Pump Challenge had to reach 2.4 or 2.1 at 5 °F, depending on their size.
A single COP is not a seasonal figure. For a whole heating season, the federal rating is HSPF2.
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