How the two compare
A gas boiler burns gas to heat water for your radiators and taps. A good one turns about 90% of the gas’s energy into useful heat. An air source heat pump works like a fridge in reverse: it takes heat from the outside air and moves it into the house, using electricity to run a compressor.
Because it moves heat rather than making it, a heat pump gives out more heat than the electricity it uses. Over a year, a typical one in a UK home gives about 2.8 units of heat for each unit of electricity.
The comparison comes down to four numbers: how much heat your home needs, the boiler’s efficiency, the heat pump’s efficiency and the prices of gas and electricity. The calculator puts them together, then adds the upfront costs and the grant.
Working out your heat demand
The heat your home needs is the same whichever system makes it. The easiest way to find it is from your gas use: multiply the kWh of gas on your annual statement by the boiler’s efficiency. A home burning 9,500 kWh of gas in a 90% boiler needs about 8,550 kWh of heat.
If you do not know your gas use, the calculator uses Ofgem’s typical figures from July 2026:
| Home | Gas a year | Heat at 90% |
|---|---|---|
| Low use (flat or small house) | 6,000 kWh | 5,400 kWh |
| Medium use (typical house) | 9,500 kWh | 8,550 kWh |
| High use (large house) | 14,000 kWh | 12,600 kWh |
An installer will do a room-by-room heat loss survey, which gives a more exact figure and decides the size of the heat pump.
Heat pump efficiency (SCOP)
A heat pump’s efficiency over a whole year is its seasonal coefficient of performance (SCOP), or seasonal performance factor when measured in a real home. A SCOP of 3 means 3 kWh of heat for each kWh of electricity.
The government’s Electrification of Heat trial measured hundreds of heat pumps in UK homes. Air source heat pumps had a median of about 2.8, and that is our starting figure. Many did better: well-designed systems running radiators at low temperatures reach 3.5 or more.
Efficiency falls when the heat pump has to heat water to a high temperature, so a system designed for low flow temperatures, with larger radiators where needed, runs more cheaply.
Gas boiler efficiency
New gas boilers in England must be at least 92% efficient under the Boiler Plus rules. In real homes they often do a little worse, because they run at higher temperatures than in tests. We assume 90%; you can change it under More options.
The boiler’s efficiency matters twice: it sets how much heat your home needs from your gas use, and how much gas a new boiler would burn. If you replace an old boiler with a new one, its running cost hardly changes in this comparison, because the heat demand is worked out from the same gas.
Gas and electricity prices
From 1 October to 31 December 2026, the Ofgem price cap for Great Britain, paying by Direct Debit, is:
| Unit rate | Standing charge | |
|---|---|---|
| Electricity (no VAT until 31 March 2027) | 26.32p per kWh | 54.83p a day |
| Gas (5% VAT) | 7.97p per kWh | 29.68p a day |
Electricity costs about 3.3 times as much as gas per unit. Per unit of heat, gas in a 90% boiler costs about 8.86p, and electricity in a heat pump with a SCOP of 2.8 about 9.40p. That gap is why the efficiency of the heat pump matters so much.
A worked example
A typical house using 9,500 kWh of gas, at the October 2026 cap, with a heat pump at the median SCOP of 2.8 and the gas supply capped.
- Heat needed9,500 kWh gas × 90%8,550 kWh
- Gas boiler: gas9,500 × 7.97p£757
- Gas boiler: standing charge29.68p × 365£108
- Heat pump: electricity8,550 ÷ 2.8 = 3,054 kWh × 26.32p£804
The heat pump is cheaper to run only because leaving gas removes the £108 standing charge. Upfront, a median heat pump at £12,908 less the £7,500 grant costs £5,408, about £2,408 more than a £3,000 boiler. At £62 a year, that does not pay back within 15 years.
Small, medium and large homes
At SCOP 2.8 and the October 2026 cap:
| Home | Gas boiler | Heat pump | Difference | 15 years: boiler | 15 years: heat pump |
|---|---|---|---|---|---|
| Low use | £587 | £508 | £79 cheaper | £11,798 | £13,022 |
| Medium use | £865 | £804 | £62 cheaper | £15,982 | £17,464 |
| High use | £1,224 | £1,184 | £40 cheaper | £21,362 | £23,174 |
The 15-year totals include a £3,000 boiler or a £12,908 heat pump less the £7,500 grant. At the median efficiency, the boiler is cheaper overall. The picture changes with a better SCOP or a cheaper electricity tariff.
Why efficiency decides it
For the medium home, the heat pump’s running cost a year at different SCOPs (the boiler costs £865):
At these prices, the heat pump matches the boiler at a SCOP of about 2.60. At 3.5 it saves £223 a year and pays back the extra upfront cost in 10.8 years; at 4.0 it saves £303 and pays back in 8.0 years. Ask installers what SCOP they design for, and how they will get there.
The gas standing charge
If you switch fully to a heat pump and have the gas supply capped, you stop paying the gas standing charge: 29.68p a day, about £108 a year at the cap. Your electricity standing charge stays the same either way.
If you keep gas for a hob, the standing charge stays. In the medium example, that turns a £62 saving into the heat pump costing £47 a year more, and raises the break-even SCOP from 2.60 to 2.97. An induction hob costs little to run: see our appliance running cost calculator.
Heat pump tariffs
Several suppliers offer tariffs for heat pump owners, with cheaper electricity at set times or a lower rate for the heat pump. Running the heat pump more in the cheap periods lowers the average price you pay.
- Heat pump a year
- £804
- Saving
- £62
- Payback
- Over 15 years
- Heat pump a year
- £611
- Saving
- £255
- Payback
- 9.5 years
- Heat pump a year
- £458
- Saving
- £407
- Payback
- 5.9 years
Check the whole tariff, not just the cheap rate: what you pay for the rest of the house’s electricity matters too. Our energy bill calculator shows your full bill.
What a heat pump costs
The government publishes the cost of every heat pump fitted under the Boiler Upgrade Scheme. From April to June 2026, the median air source heat pump cost £12,908 before the grant. A quarter cost less than £11,128 and a quarter more than £15,627.
The price usually includes the heat pump, a hot water cylinder, controls, and any radiators that need upsizing. Homes with a combi boiler and no cylinder need room for one. A replacement gas boiler is cheaper: we use £3,000 as an example, but enter your own quote. If your boiler is fine for now, set the boiler cost to £0.
The Boiler Upgrade Scheme
In England and Wales, the Boiler Upgrade Scheme gives:
- £7,500 towards an air source or ground source heat pump.
- £2,500 towards an air-to-air heat pump.
- £5,000 towards a biomass boiler.
- An extra £1,500 until March 2027 for an air or ground source heat pump in a home heated by oil or LPG with no mains gas.
The installer applies and takes the grant off your bill. The installer must be MCS certified, and the home normally needs a valid Energy Performance Certificate. Without the grant, the medium example’s extra upfront cost rises from £2,408 to £9,908.
Scotland, Wales and Northern Ireland
Wales is covered by the Boiler Upgrade Scheme. Scotland is not: Home Energy Scotland offers its own grant and an interest-free loan for heat pumps. Northern Ireland has no equivalent grant, and its energy prices are not covered by the Ofgem cap, so enter your own rates.
0% VAT until March 2027
Installing a heat pump in a home in Great Britain is zero-rated for VAT until 31 March 2027. From 1 April 2027, the rate is due to return to 5%. On a £12,908 heat pump, that would add about £645.
Electricity VAT
Household electricity also carries no VAT from 1 October 2026 to 31 March 2027, which lowers heat pump running costs. Gas keeps 5% VAT. If electricity VAT returns at 5% in April 2027, heat pump running costs rise by about 5%.
Payback and the 15-year view
Payback is the extra upfront cost divided by the yearly saving. If the heat pump costs less upfront than the boiler after the grant, it pays back from day one. If it costs more to run, it never pays back.
A large home with a well-designed system (SCOP 3.5) saves £277 a year and pays back in 8.7 years; over 15 years it costs £19,621 against the boiler’s £21,362. Price changes matter too: if gas and electricity both rose 3% a year, the medium example’s 15-year totals would be £19,097 for the boiler and £20,356 for the heat pump.
Carbon
Using the government’s 2026 conversion factors (0.182 kg of CO2e per kWh of gas and 0.144 kg per kWh of grid electricity, including losses), the medium home’s boiler produces about 1.7 tonnes of CO2e a year and the heat pump about 440 kg: a cut of about 1.3 tonnes, or three quarters.
As the grid gets cleaner each year, the heat pump’s carbon falls further. A gas boiler’s does not.
Is your home suitable?
- Insulation: loft and wall insulation reduce the heat needed and let the heat pump run at lower, more efficient temperatures.
- Radiators: some may need to be larger. Underfloor heating suits heat pumps well.
- Space: an outdoor unit (usually beside or behind the house) and a hot water cylinder indoors.
- Noise and planning: most air source heat pumps are permitted development in England if they meet the size and noise rules. Check with your council for flats, listed buildings and conservation areas.
Adding solar panels
Solar panels make most of their power in summer, when a heat pump needs least. They still help with hot water and spring and autumn heating, and with a battery or a smart tariff the two can work well together. See what panels would make on your roof with our solar panel calculator.
Living with a heat pump
Heat pumps work best running steadily at a lower temperature, rather than blasting heat in the morning and evening like a boiler. Radiators feel warm rather than hot. Many people leave the heating on low all day and set the hot water to heat once or twice a day.
Servicing is recommended once a year, as with a boiler. Both systems typically last 15 years or more. If you are planning a move, our moving house budget helps you plan the costs.
Next steps
- Find your gas use from your annual statement and enter it.
- Get quotes from at least two or three MCS-certified installers, with a heat loss survey.
- Ask for the expected SCOP and flow temperature in writing.
- Check the grant: the installer applies for the Boiler Upgrade Scheme.
- Compare tariffs for heat pump owners before switching.
- Plan the timing: 0% VAT runs to 31 March 2027.