Heat Pump Calculator
COP, running cost, and the Carnot ceiling above it.
Work out Heat Pump. COP, running cost, and the Carnot ceiling above it. Answers in the units the job actually uses.
Electrical input at design
2.29 kW
SCOP 4.38 · 53% of the Carnot limit
A heat pump moves heat rather than making it, which is why its coefficient of performance exceeds 1. Three-and-a-half means three and a half kilowatts of heat for every kilowatt of electricity — the other two and a half come from outside, for free. The Carnot limit is the theoretical ceiling set by the temperature difference, and it is worth showing because of how steeply it rises as the gap narrows. Moving from a 45 °C flow to 35 °C lifts the ceiling substantially, which is why underfloor heating and oversized radiators pay for themselves in running cost. Seasonal COP exceeds the design-day figure because most of the heating season is milder than the coldest day. The uplift used here is a reasonable approximation; a manufacturer's SCOP figure from a proper bin analysis is better if you have one.
How the Heat Pump Calculator works
Electrical input, seasonal COP and running cost against a gas boiler, with the Carnot limit for the temperatures involved. That limit is worth seeing, because it rises steeply as the flow temperature comes down.
Also known as: heat pump running cost vs gas · what is a good scop · is a heat pump cheaper than gas · heat pump electricity per year
Frequently asked questions
What is a COP?
Coefficient of performance: heat delivered divided by electricity consumed. A COP of 3.5 means 3.5 kW of heat per kW of electricity — the rest is moved from outside rather than created.
What is the difference between COP and SCOP?
COP is measured at one set of conditions, usually the design day. SCOP averages across a whole heating season and is higher, because most of the season is milder than the coldest day.
Why does flow temperature matter so much?
Because the theoretical ceiling on efficiency depends on the temperature gap. Dropping from 45 °C to 35 °C flow lifts the Carnot limit substantially, and real COP follows — which is why underfloor heating and oversized radiators pay for themselves.
Is a heat pump cheaper to run than gas?
It depends entirely on the ratio of electricity to gas prices and on the SCOP achieved. At a SCOP of 3.5 a heat pump breaks even with a 90% gas boiler when electricity costs about 3.9 times gas per kWh.
What is the Carnot limit?
The maximum efficiency thermodynamics allows for moving heat between two temperatures. Real heat pumps reach 40 to 55% of it. It is not a target, but it explains exactly why lower flow temperatures help.
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