Heat Pump COP Calculator
Enter HSPF, outdoor temperature and your rate to get the COP the heat pump actually delivers at that temperature, its derated capacity, and the cost per kWh of heat vs resistance.
Last updated: 2026-09-28
How the calculation works
- HSPF converts to a seasonal COP by unit conversion: BTU/Wh × 0.2931 (Wh→W).
- Air-source COP falls as outdoor temperature drops — roughly 2.8% per °C below 8 °C, floor at ~35% of rating.
- Capacity derates too: the heat the pump can deliver shrinks as it gets colder, which is when backup strips engage.
- Cost per kWh of heat divides the electric rate by COP — resistance heat is always COP 1.0, the comparison baseline.
Formula
COP_seasonal = HSPF × 0.2931 COP(T) ≈ COP_seasonal × [1 − 0.028 × max(0, 8.3 − T)] Cost per kWh heat = rate ÷ COP
| Symbol | Meaning | Unit |
|---|---|---|
COP | Coefficient of performance (heat out ÷ electric in) | — |
HSPF | Heating Seasonal Performance Factor | BTU/Wh |
Worked example
Interpreting the result
The balance point is the practical limit: as capacity derates and the house load rises with cold, they cross — below it, resistance strips carry the remainder and real seasonal COP lands between the heat pump's and 1.0. Cold-climate units push the balance point down with inverter compressors and vapor injection. Against gas, compare cost per kWh of heat: gas at 85% AFUE and $1.20/therm delivers heat at about $0.041/kWh — competitive only where electricity is cheap or the heat pump's COP is high.
Assumptions
- Linear COP derate below 8.3 °C — an approximation of inverter and fixed-speed air-source behavior.
- HSPF (Seasonal) as the starting point; HSPF2 ratings run ~10% lower numerically for the same unit.
Limitations
- Ground-source (geothermal) heat pumps derate far less — this model overstates their cold-weather penalty.
- Defrost cycles, auxiliary heat lockouts and duct losses are not modeled.
Frequently asked questions
What COP does a heat pump have at 0 °F?
Modern cold-climate units maintain COP 1.5-2.0 at −18 °C; standard units drop toward 1.2-1.5. Below that, output and COP fall together until backup resistance takes over.
How do I convert HSPF to COP?
Multiply HSPF by 0.2931. An HSPF 10 unit: seasonal COP 2.93. It is a pure unit conversion — HSPF is BTU of heat per Wh of electricity, COP is the same ratio unitless.