This is the question everyone asks and it usually gets a vague answer. Here is the arithmetic, with the numbers shown, so you can judge it yourself.
The short answer: at current prices, a typical heat pump costs about the same to run as the gas boiler it replaces. A well-designed one saves meaningfully. A poorly designed one costs more.
We are aware that is not the answer the industry usually gives.
The arithmetic
Two numbers do all the work.
Electricity costs about 26.32p per unit. Gas costs about 7.97p. So electricity is roughly three and a third times the price of gas.
A gas boiler is not 100% efficient. A good condensing boiler runs at around 85% over a year in a real house, so the heat it delivers costs more than the gas price suggests:
Gas price ÷ boiler efficiency = cost per unit of heat
A heat pump delivers several units of heat per unit of electricity. That multiple, measured over a whole year in a real installation, is the seasonal performance factor, or SPF:
Electricity price ÷ SPF = cost per unit of heat
What that gives you
| Cost per kWh of heat | |
|---|---|
| Gas boiler at 80% efficiency | 9.96p |
| Gas boiler at 85% efficiency | 9.38p |
| Gas boiler at 90% efficiency | 8.86p |
| Heat pump at SPF 2.5 | 10.53p |
| Heat pump at SPF 2.8 | 9.4p |
| Heat pump at SPF 3.0 | 8.77p |
| Heat pump at SPF 3.5 | 7.52p |
| Heat pump at SPF 3.86 | 6.82p |
The break-even against a gas boiler at 85% is an SPF of about 2.81.
Prices from the Ofgem price cap, 1 Oct 2026 to 31 Dec 2026. Checked 4 Nov 2026.
So what SPF do real heat pumps achieve?
This is where the honesty is needed.
- The Energy Systems Catapult monitored 291 UK air source heat pump systems in its Electrification of Heat trial and found a median SPF of 2.8 in its interim results.
- The middle half of those systems ran between 2.53 and 3.09. Some do much better, usually ones designed and set up to run at low flow temperatures.
Compare the field median of 2.8 with the break-even of 2.81. That is why the honest answer is “about the same”.
The datasheet figure is not the real figure
Manufacturers publish a SCOP, a seasonal coefficient of performance measured under laboratory conditions. Real installed performance, the SPF, is usually lower.
If a quote bases a running cost saving on a SCOP of 4.5, ask what SPF they expect in your house and why. A good installer will have a view and will explain it. A poor one will repeat the datasheet.
Sources: Energy Systems Catapult, Electrification of Heat interim insights; RECC performance data research. Checked 4 Nov 2026.
What the table leaves out, in your favour
The gas standing charge If you remove your gas connection entirely, you stop paying it. That is a fixed saving every single day regardless of how much heat you use, and it is not in the per-unit comparison above. For a household using relatively little heat it can be the difference on its own.
If you keep gas for a hob, you keep paying it. Worth factoring in when you decide about the cooker.
A time-of-use tariff A heat pump running more in cheaper periods lowers its effective electricity price. This requires a well-controlled system and a suitable tariff, and it is not automatic. See smart tariffs.
Solar Electricity you generate yourself costs you nothing at the point of use. This is the largest single thing you can do to change the comparison, and it is why solar and a heat pump together is a stronger proposition than either alone.
What determines whether yours lands at 2.5 or 3.5
Installation quality, more than the brand of the unit.
- Flow temperature. The single biggest factor. A system designed to run at 35 to 45 degrees performs far better than one running at 55.
- Radiator sizing. Bigger radiators allow lower flow temperatures.
- Sizing of the heat pump itself. An oversized unit cycles on and off and loses efficiency.
- Controls, and how they are set. Weather compensation, and being left to run steadily rather than switched on and off like a boiler.
- Insulation. No longer required for the grant, still determines how much heat you need.
- The heat loss calculation. Ask to see it. A proper room-by-room calculation for your house is the best single indicator of a competent installer.
What we would say
Do not buy a heat pump expecting your bills to fall automatically. Buy one because you want to move off fossil fuel heating, because the grant makes the capital cost reasonable, because you are getting rid of the gas standing charge, or because you have or are getting solar, which changes the sums.
And then spend your effort on choosing an installer who will design it properly, because that is what decides which row of the table above you end up in.