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Heat pump or gas: running cost over a year

From the gas on your bill to the cost of a heat pump: useful heat, electricity, spending over a year and the JAZ at which the two costs break even.

Updated 13 Oct 2026 · KilowattTally

Your boiler and the heat pump

The kWh on your annual gas bill.

I only have cubic metres

Look on the annual bill for the consumption in kWh, usually next to the cubic metres read at the meter: the calculator works in kWh. If gas is also used for cooking, the calculation attributes all of it to heating.

Share of the gas kWh that becomes useful heat in a year.

I do not know it

Few people really know it. Try two values, for example 80 and 95: the result shows how much it matters. The home’s useful heat is gas kWh × efficiency, and the heat pump must deliver the same heat.

Price per kWh of your contract.

The one you would no longer pay if the gas supply were disconnected.

Heat produced ÷ electricity used in a year.

Where do I find it?

For a heat pump already running: heat and electricity from the meters, over a full year. For a planned one: the datasheet gives the SCOP, calculated under standard test conditions for the flow temperature stated next to it (lower with underfloor heating, higher with radiators); in real use the value depends on the house. Fraunhofer ISE measured values from 2.6 to 4.9, averaging 3.4, in 61 existing houses with air-to-water heat pumps.

Price per kWh of the tariff the heat pump would use.

Only if the heat pump has a separate meter.

Result

Enter gas, efficiency, prices and JAZ to compare the running cost over a year.

Useful heat is the gas used times the boiler efficiency; the heat pump must deliver the same heat, hot water included if the boiler made it. One JAZ for the whole year; standing charges only if you enter them. Prices constant over the year; no purchase price, incentive or loan. Where the values come from and what the calculation leaves out

Background

The calculator starts from what you already know: how much gas you burned in a year. Multiplied by the boiler efficiency, this gives the heat the house actually used. The heat pump has to deliver the same heat; how much electricity it needs depends on its annual performance factor, the JAZ. With your gas and electricity prices, the result is a year’s spending with each one.

How to use it

  1. Enter the kWh of gas from your last annual bill and the boiler’s average efficiency. If you do not know it, try two values: the result shows how much it matters.
  2. Enter the gas price and, if you like, the standing charge you would no longer pay if the gas supply were disconnected.
  3. Enter the JAZ and the electricity price for the heat pump, with the standing charge for the separate meter if there will be one.

How to read the result

  • Difference in a year: spending with gas minus spending with the heat pump, standing charges included only if you entered them.
  • Break-even JAZ: the performance factor at which the two costs are equal. If the JAZ you expect is well above it, the electricity price and the boiler efficiency make little difference to the comparison; if it is close, they make a lot of difference.
  • The table repeats the sum with JAZ from 2.5 to 5, because the real JAZ is only known after a year of operation. Fraunhofer ISE measured values from 2.6 to 4.9 in 61 existing houses with air-to-water heat pumps, with an average of 3.4 [7]; in a public British trial of 428 air-to-water heat pumps the average was about 2.8 [11].

An example

With 20,000 kWh of gas, a 90% boiler, gas at 11.93 ct/kWh and electricity at 37 ct/kWh, the 2026 BDEW averages for single-family houses and for households [9] [8], open the example in the calculator: with the average JAZ measured by Fraunhofer ISE, 3.4, the heat pump would use about 5,294 kWh and cost about €427 less in a year; the two costs break even at a JAZ of about 2.8.

What it does not tell you

The comparison covers only the running cost. Purchase price, incentives, loans, maintenance and payback time are left out, as are sizing and installing the heat pump. The assumptions are in method and sources; what JAZ, SCOP and COP mean is in JAZ, SCOP and COP.

Sources

  1. Wärmepumpen heizen auch im Altbau klimafreundlich: Forschungsprojekt abgeschlossen (comunicato stampa, 3 novembre 2025) — Fraunhofer ISE, retrieved 13 Oct 2026
  2. BDEW-Strompreisanalyse Herbst 2026 — BDEW Bundesverband der Energie- und Wasserwirtschaft, retrieved 13 Oct 2026
  3. BDEW-Gaspreisanalyse August 2026 — BDEW Bundesverband der Energie- und Wasserwirtschaft, retrieved 13 Oct 2026
  4. Electrification of Heat: analisi dei dati di monitoraggio — OpenEnergyMonitor, retrieved 13 Oct 2026