Coefficient of performance (COP)

COP is the most direct measure of heat pump efficiency. Electric resistance heaters turn electricity into heat at a COP of 1. Heat pumps move existing heat rather than create it, so their COP is above 1, but it falls as the temperature difference between source and destination grows. A Canadian government field study of a cold-climate air-source heat pump, for example, measured heating COP from about 1.5 at −21 °C to about 3.0 at around +5 °C outdoors. Seasonal metrics (SCOP, HSPF2, SEER2) average this kind of performance over a climate's year.

For controls and energy products, COP is the number to improve: lower supply-water temperatures, smarter defrost, variable-speed operation, right-sizing and avoiding backup resistance heat all raise real-world COP.