What is COP for a heat pump?

COP (Coefficient of Performance) is the ratio of useful heat (or cooling) delivered to the electrical energy consumed. A COP of 3 means the pump delivers 3 kWh of heat for every 1 kWh of electricity used.

Carnot COP is the theoretical maximum efficiency any heat pump can achieve between two given temperatures. Real heat pumps reach roughly 40–60% of this limit due to friction, heat exchanger losses, and compressor inefficiency.

How does outdoor temperature affect heat pump efficiency?

As the source temperature drops (e.g., cold winter air), the temperature difference between source and sink widens, which lowers the Carnot COP. This is why heat pumps work best in mild climates or with ground-source setups.

What is a good real-world COP?

Modern air-source heat pumps achieve COP 2.5–4 in heating mode at 7°C outdoor air. Ground-source (geothermal) units typically achieve COP 3.5–5. Any COP above 1 is more efficient than direct electric resistance heating.

How is cooling COP different from heating COP?

In cooling mode the heat pump removes heat from the cooled space and dumps it outside. The cooling COP formula is T_cold / (T_hot − T_cold) in Kelvin, which is always one less than the heating COP for the same temperature pair.

Heat Pump Efficiency Calculator

Enter source and sink temperatures to get the theoretical Carnot COP and estimated real-world COP for your heat pump in heating or cooling mode.

Inputs

Mode

Temperature Unit

Source Temperature (outside air / ground)

°C

Typical outdoor air: −10 °C to 20 °C

Sink Temperature (indoor delivery / hot water)

°C

Typical underfloor heating: 35–45 °C; radiators: 55–70 °C

Real-world Efficiency Factor 50%

30% (older/budget) 70% (premium inverter)

Theoretical Carnot COP

Maximum possible efficiency — no real machine can exceed this.

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Estimated Real-world COP

Based on your efficiency factor applied to the Carnot limit.

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Summary

This heat pump efficiency calculator uses the Carnot thermodynamic cycle to find the theoretical maximum Coefficient of Performance (COP) for any source-to-sink temperature pair. It then applies a realistic efficiency factor to give a practical COP estimate, helping you understand how temperature conditions and mode (heating vs. cooling) affect energy consumption.

How it works

Select heating or cooling mode depending on your heat pump application.
Enter the source temperature (outside air, ground, or water) in °C or °F.
Enter the sink temperature (indoor air or hot water supply) in °C or °F.
The calculator converts both values to Kelvin and applies the Carnot COP formula.
A real-world COP estimate (typically 40–60% of Carnot) is shown alongside the theoretical maximum.
Use the results to compare equipment specs or estimate seasonal energy costs.

Use cases

Compare the theoretical efficiency of air-source vs. ground-source heat pumps.
Estimate how much electricity a heat pump will use at different outdoor temperatures.
Understand why heat pump efficiency drops in very cold winter weather.
Size a heat pump system based on required COP for a given climate zone.
Validate a manufacturer's COP claim against the Carnot theoretical maximum.
Teach thermodynamics concepts — Carnot cycle and second law of thermodynamics.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu