What is COP? Coefficient of performance explained
COP (coefficient of performance) is how many units of heat a heat pump delivers per unit of electricity it consumes. A COP of 3 means each kWh of electricity moves 3 kWh of heat - effectively 300% efficient, versus 100% (COP 1.0) for electric resistance. COP falls as it gets colder; the seasonal average is what drives your bill.
Why COP can exceed 100%
A heat pump does not create heat - it moves it from outdoor air (or ground) into your home, using electricity only to run the compressor and fans. Because it moves more energy than it consumes, COP is typically 2-4. Electric resistance, by contrast, converts electricity to heat one-to-one (COP 1.0).
Instantaneous vs seasonal COP
The rated COP is at one test temperature; real COP drops on cold days. The seasonal COP averages performance across the winter and is what we use to estimate annual cost. This site uses seasonal COP presets of 2.0 (very cold) to 3.2 (mild).
COP and your bill
Heating cost equals heat demand divided by (3,412 times COP) times electricity price. Doubling the COP halves the electricity needed. That is why even in high-electricity states a heat pump usually beats electric resistance, propane and oil.
| System | Effective COP |
|---|---|
| Electric resistance / baseboard | 1.0 |
| Air-source heat pump (very cold winter) | about 2.0 |
| Air-source heat pump (cold) | about 2.4 |
| Air-source heat pump (mixed) | about 2.8 |
| Air-source heat pump (mild) | about 3.2 |
| Ground-source (geothermal) | 3.5-4.5 |
Source: Industry references (AHRI/DOE/ENERGY STAR). Data as of June 2026.
Frequently asked questions
What COP should I assume?
For a modern cold-climate air-source heat pump, 2.4 in a cold climate, 2.8 in a mixed climate and 3.2 in a mild one are reasonable seasonal planning values. Geothermal is higher. Use the calculator to test your own number.
Does COP change with temperature?
Yes. COP is highest in mild weather and falls as the outdoor temperature drops, because the heat pump has to work harder to extract heat. Cold-climate models are designed to hold a useful COP into the teens (F).
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Last updated: 2026-06-29