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Enter the gas you use per year, the efficiency of your boiler, the efficiency of the heat pump (seasonal performance factor) and the prices. You see the heat your home needs, the electricity the heat pump uses for it, both costs, and the difference.

Enter your values

From your yearly gas bill, in kWh.
Where do I find this?

Your last yearly gas bill shows the consumption in kWh. If it only shows m³, use the Gas m³ to kWh Calculator. One winter can be unusually cold or mild: the average of two or three years is more reliable.

Heating with oil? Enter litres × 10 here and the oil price per kWh below, or use the Heating Oil to Heat Pump Calculator.

Heat delivered per kWh of electricity over a year. Measured in existing houses: about 3.3 on average for air source, 3.6 to 5.2 for ground source.
Where do I find this?

The Jahresarbeitszahl (JAZ) is the yearly heat output divided by the yearly electricity input. Your installer gives an estimate for your house.

In a Fraunhofer ISE field test in existing houses (2022/23), air-source heat pumps reached 3.3 on average (2.4 to 4.0) and ground-source heat pumps 3.6 to 5.2. A lower flow temperature, for example with underfloor heating or large radiators, gives a higher value. 3.3 is an example.

Per kWh. Heat pump tariffs are often cheaper than normal household tariffs.
Where do I find this?

Use the price per kWh of your heat pump or household tariff from the contract or bill. 25 ct = 0.25.

Per kWh of gas. Use the oil price per kWh if you heat with oil.
Where do I find this?

Look for 'Arbeitspreis' or 'price per kWh' on your gas bill. For oil, divide the price per litre by about 10.

Share of the gas that ends up as heat in the house over a year. Often 80 to 95 %.
Where do I find this?

Older boilers are lower, modern condensing boilers higher. 90 is an example.

Data sheets of condensing boilers often state more than 100 %: that figure refers to the net calorific value. With the kWh of a gas bill, which use the gross calorific value, about 85 to 95 % is realistic for a condensing boiler.

Only changes the symbol; no exchange rate is applied.

Result

Enter your values to see the result.

Heat pump saves per year
– (negative = costs more)
Heat pump cost per year
–
Boiler cost per year
–
Heat pump electricity
– kWh
Heat your house gets
– kWh

Want this tracked for you? UtilityControl logs your meters and costs automatically.

How it is calculated

  • Heat your house gets (kWh) = gas used × boiler efficiency ÷ 100
  • Heat pump electricity (kWh) = heat ÷ seasonal performance factor
  • Costs: gas = gas used × gas price; heat pump = electricity × electricity price; saving = gas cost − heat pump cost

Example

15,000 kWh of gas in a boiler with 90 % efficiency give 13,500 kWh of heat. A heat pump with a factor of 3.3 needs 13,500 ÷ 3.3 = 4,091 kWh of electricity for it: 1,023 at 0.25. The gas costs 15,000 × 0.10 = 1,500, so the heat pump saves about 477 a year.

What this estimate leaves out

The result depends strongly on the real performance factor, which depends on the house and the flow temperature. The fixed gas fee you would no longer pay, investment, grants, maintenance and price changes are not included.

Sources: Fraunhofer ISE: heat pump field test in existing buildings, 2024 (in German)

Written and reviewed by QLines, Cologne · Last reviewed

Guide: COP, SCOP and the seasonal performance factor explained

FAQ

Frequently Asked Questions

How much electricity does a heat pump use?

Divide the heat the house needs by the seasonal performance factor. From a gas bill: 15,000 kWh of gas in a 90 % boiler give 13,500 kWh of heat, so a heat pump with a factor of 3.3 uses about 4,100 kWh of electricity a year.

What is the Jahresarbeitszahl (JAZ)?

The seasonal performance factor: the heat the heat pump delivers over a year divided by the electricity it uses. A value of 4 means one kWh of electricity gives four kWh of heat. In a Fraunhofer ISE field test in existing houses, air-source heat pumps averaged 3.3 (2.4 to 4.0) and ground-source heat pumps reached 3.6 to 5.2.

Is a heat pump cheaper to run than a gas boiler?

It is cheaper to run while the electricity price stays below the gas price × performance factor ÷ boiler efficiency. With a factor of 3.3 and a 90 % boiler that is about 3.7 times the gas price: at 0.10 per kWh of gas, up to about 0.37 per kWh of electricity.

Where do I find my gas use?

On your last yearly gas bill, in kWh. Use the average of two or three years if one winter was unusually cold or mild. For oil, a litre is about 10 kWh.

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