C.O.P. / Coefficient of performance

COP, or coefficient of performance, is a heat pump efficiency measure for a specific set of operating conditions. It compares useful heat output with the electrical energy used by the heat pump at that moment, so a COP of 3 means the unit is delivering about 3 kWh of heat for every 1 kWh of electricity it consumes under those conditions. The figure changes with outdoor temperature, flow temperature and the heat demand being met, which is why a single COP number should not be treated as a seasonal running-cost forecast. UK heat pump paperwork may also show SCOP or SPF, which look at performance across a defined season or annual pattern rather than one test point.