Ratings & Efficiency
What Is COP?
COP (Coefficient of Performance) is the ratio of heat energy a system moves to the energy it consumes, measured at one operating condition. A COP of 4 means four units of heat delivered per unit of electricity used. Because heat pumps move heat rather than create it, their COP is greater than 1.
Also called: Coefficient of Performance
Why it matters to you
COP is the headline number for geothermal, where it is quoted at standard loop temperatures and is typically higher than an air-source heat pump's, because the ground stays at a steadier temperature than coastal air. It is a single-point rating, so it is a fair way to compare two systems at the same condition and a poor way to predict a whole season.
What to do about it
When comparing geothermal quotes, check that both COP figures are quoted at the same entering water temperature — otherwise you are comparing different tests. For air-source equipment, seasonal ratings (HSPF2) describe the heating season better than COP does.
Common questions
- What is a good COP?
- It depends entirely on the condition quoted. Electric resistance heat has a COP of 1 by definition — every watt in becomes a watt of heat. Any heat pump above 1 is moving more heat than the energy it consumes. Because COP varies with source temperature, a figure without its test condition attached is not meaningful.
- Why is geothermal COP usually higher?
- Because the heat source is more stable. An air-source heat pump has to pull heat from outdoor air that may be near freezing on a January morning; a ground loop draws from earth that holds a much steadier temperature year-round. The smaller the temperature difference the system works across, the less energy it takes to move heat.
- How does COP relate to HSPF2?
- HSPF2 is effectively a seasonal, weighted version of the same idea, expressed in different units. COP is dimensionless and instantaneous; HSPF2 blends many operating hours into one figure. Use COP to compare equipment at a stated condition, and HSPF2 to think about a whole heating season.
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