Heat Pump COP Efficiency Calculator
The coefficient of performance, or COP, measures how efficiently a heat pump delivers heat. It is the ratio of useful heat output to the electrical energy the pump consumes, so a COP of 3 means three units of heat moved per unit of electricity. Because a heat pump transfers ambient heat rather than burning fuel, COP is normally greater than one. This calculator returns the measured COP from your heat output and electrical input, the ideal Carnot COP set by the source and delivery temperatures, and the second-law efficiency that shows how close the machine runs to its thermodynamic limit. Enter your own measured values; performance falls as the temperature lift grows.
Heat pump COP formula
Measured COP = heat output / electrical input
T_hot (K) = delivery deg C + 273.15
T_cold (K) = source deg C + 273.15
Carnot COP = T_hot / (T_hot - T_cold)
Second-law efficiency = measured COP / Carnot COP * 100
The Carnot COP is the heating-mode upper bound between the two temperatures. Real machines reach a fraction of it because of compressor, heat-exchanger, and defrost losses.
Heat pump efficiency context
- COP greater than one is normal because a heat pump moves ambient heat rather than creating it.
- COP falls as the temperature lift between source and delivery increases.
- The Carnot COP can never be exceeded; it rises sharply as the lift approaches zero.
- Seasonal ratings (SCOP, HSPF) average performance across a range of outdoor conditions.
- Defrost cycles and auxiliary resistance heat in cold weather lower the effective COP.
Heat pump COP: frequently asked questions
What is the coefficient of performance (COP)?
COP is the ratio of useful heat delivered to the electrical energy consumed: COP = heat output / electrical input. A COP of 3 means the heat pump moves three units of heat for every unit of electricity it draws, because it transfers ambient heat rather than generating heat directly.
What is the Carnot COP and why does it matter?
The Carnot COP is the maximum theoretical heating efficiency between two temperatures: COP = T_hot / (T_hot - T_cold), with temperatures in kelvin. It sets an upper bound no real heat pump can exceed. The closer a real COP is to the Carnot value, the better the machine performs against the thermodynamic limit.
What is a good heat pump COP?
It depends on the temperature lift between the source and the heated space. Smaller lifts give higher COP. Many air-source heat pumps deliver a COP between 2 and 4 in mild conditions, with COP falling as the outdoor temperature drops. Enter your own measured figures for an accurate result.
How does COP relate to SCOP and HSPF?
COP is an instantaneous ratio at fixed conditions. SCOP (seasonal COP) and the US HSPF rating average performance across a heating season and a range of temperatures. This calculator computes a point COP from the values you supply; seasonal ratings come from standardised test procedures.
Why are temperatures converted to kelvin for the Carnot COP?
The Carnot relationship is defined on the absolute temperature scale. Add 273.15 to a Celsius temperature to get kelvin. Using Celsius or Fahrenheit directly would give a meaningless ratio, so the calculator converts your Celsius inputs to kelvin before computing the ideal COP.
Official sources
- U.S. Department of Energy: Heat Pump Systems.
- ENERGY STAR: heating and cooling efficiency programs.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.