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Heat pump vs gas boiler: the running-cost maths for 2026
At the July 2026 Ofgem cap, electricity is 3.56 times the price of gas per kWh. That single ratio decides whether a heat pump is cheaper to run than a condensing boiler. Here is the arithmetic, and where it breaks.
Almost every argument about heat pumps in the UK is really an argument about one number. Under the Ofgem price cap for 1 July to 30 September 2026, electricity costs 26.11p per kWh and gas costs 7.33p per kWh. Divide one by the other and you get 3.56.
That is the ratio a heat pump has to beat. If it produces more than 3.56 kWh of heat per kWh of electricity, it is cheaper to run than gas burned at 100 % efficiency. A condensing boiler is not 100 % efficient — call it 90 % over a season — so the honest threshold is 3.56 × 0.90 = 3.20.
What field SCOPs actually are
A datasheet SCOP of 4.2 is measured at a 35 °C flow temperature. Almost no retrofit runs at 35 °C, because existing radiators were sized for 75 °C water. Radiator output falls roughly with the 1.3 power of the temperature difference to the room, so at 50 °C a radiator gives about 63 % of its catalogue output. If your radiators were sized with no margin, the system has to run hotter, and the SCOP falls with it:
| Design flow temperature | Realistic SCOP | Cost per kWh of heat | Verdict vs a 90 % gas boiler |
|---|---|---|---|
| 35 °C, underfloor throughout | 3.9 | 6.7p | Cheaper |
| 45 °C, deliberately oversized radiators | 3.4 | 7.7p | Roughly level |
| 50 °C, existing radiators, worst ones swapped | 3.0 | 8.7p | More expensive |
| 55 °C, existing radiators untouched | 2.8 | 9.3p | More expensive |
Gas at 7.33p and 90 % seasonal efficiency delivers heat at 8.1p per kWh. So the crossover sits between 45 °C and 50 °C — which is exactly where most British retrofits land, and exactly why the public argument never resolves.
Assumptions behind these figures
- Electricity £0.2611/kWh, gas £0.0733/kWh — Ofgem cap, direct debit, 1 July – 30 September 2026
- Condensing boiler seasonal efficiency 90 %
- SCOP by flow temperature as published in data/energy-prices.json
- Unit rates only in the per-kWh column; standing charges handled separately below
The three things that move the answer
A heat pump tariff. Heat-pump-specific and time-of-use tariffs price a large share of heating consumption below the cap. Moving from cap-rate electricity to a tariff averaging 20p/kWh cuts the break-even SCOP from 3.20 to 2.46, which every competent installation clears.
Emitter work. Upsizing the three or four worst radiators is usually a few hundred pounds and buys 5 °C of flow temperature — about 0.2 on the SCOP. That is a better return per pound than most fabric measures.
Standing charges. Removing gas entirely saves the gas standing charge, 29.04p a day — £106 a year. That is not a rounding error; it is the difference between two of the rows in the table above.
Where a heat pump wins without argument
Off the gas grid, none of this is close. Direct electric heating delivers heat at 26.11p per kWh, which any heat pump beats by a factor of nearly three. Heating oil and LPG are both far above mains gas per kWh, and off-grid oil and LPG homes now get £9,000 in total from the Boiler Upgrade Scheme rather than £7,500 — see the oil and LPG uplift.
What to do with this
Ask any installer for the design flow temperature before you compare prices. It is the number that determines your bill, it takes them ten seconds to state, and a quote that does not contain it is not a design. Then put your own consumption into the running-cost calculator, which shows every step of this arithmetic with your figures instead of these.
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Compare at least three installers. Ask each one for the heat-loss calculation and the design flow temperature in writing — that number decides your running cost more than the brand on the box.
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Questions people ask
Is a heat pump cheaper to run than a gas boiler in the UK in 2026?
It depends on the design flow temperature. At the July 2026 price cap a heat pump needs a seasonal efficiency above about 3.2 to beat a 90 % efficient condensing boiler. Systems designed for 35–45 °C flow clear that; systems left on existing radiators at 55 °C generally do not, unless you move to a heat pump electricity tariff.
What is the break-even SCOP against gas?
Electricity 26.11p divided by gas 7.33p is 3.56, multiplied by the boiler's 90 % seasonal efficiency gives a break-even SCOP of about 3.2.