What do input and output mean on a heat pump?

Q: What do input and output mean on a heat pump?

Input is the electricity the heat pump uses, which is what you pay for. Output is the heat it delivers to your radiators and hot water. Both are in kWh (kilowatt-hours), and output divided by input is the COP.

Updated 29 September 2026

Short answer: input is the electricity the heat pump uses, which is what you pay for. Output is the heat it delivers to your radiators and hot water. Both are in kWh (kilowatt-hours), and output divided by input is the COP.

If you used 10 kWh of electricity (input) and the heat pump delivered 32 kWh of heat (output), its COP was 3.2 for that time. The extra 22 kWh came from the outside air, free.

Input drives your bill. Output tells you how much heat the house needed. On a cold week both go up, which is why a higher bill in winter doesn't mean the heat pump is doing worse. It may just be doing more.