Heat Pump vs Gas Boiler in the UK

On the price cap for 1 October to 31 December 2026, an air source heat pump matches a 90% efficient gas boiler on running costs at a seasonal efficiency of 2.97, and beats it above that. Upfront, the Energy Saving Trust puts a typical heat pump installation at around £12,000 and a gas boiler replacement at £3,500, so after the £7,500 Boiler Upgrade Scheme grant in England and Wales you are comparing roughly £4,500 with £3,500. That is a gap of about £1,000, not the £8,000 most people assume. The question that decides whether switching saves you money is therefore not the price of the kit. It is whether your installed system will run above or below a seasonal efficiency of three, and that is settled by your radiators and your flow temperature.

The break-even is a seasonal efficiency of 2.6 to 3.0, depending on the boiler you are replacing

Divide the electricity price by the gas price and you get the efficiency a heat pump has to hit to break even. Ofgem's published cap rates for 1 October to 31 December 2026, Direct Debit, Great Britain average, are electricity at 26.32p per kWh with a 54.83p daily standing charge and gas at 7.97p per kWh with a 29.68p daily standing charge. Electricity is 3.30 times the price of gas per unit this quarter.

A gas boiler does not turn every unit it burns into heat in your rooms, and nor does a heat pump deliver only one unit of heat per unit of electricity. So the comparison has to be made per kWh of heat delivered into the house:

Read that table the other way round and it tells you something more useful than any savings estimate. A heat pump at a seasonal efficiency of 2.5 costs more to run than any gas boiler in the table. A heat pump at 3.5 is cheaper than all of them by about 15%. The entire argument lives in that band, and nothing about the brand on the outdoor unit puts you at one end of it rather than the other. Flow temperature does, which means radiator sizing does, which is why our guide to radiators and heat pumps is the one worth reading before you take a quote.

The efficiency printed on a manufacturer's datasheet is a laboratory figure measured at a stated flow temperature, usually 35°C, and it falls as the flow temperature rises. On Mitsubishi's own datasheet for its 12kW Ecodan R290, the same machine is rated 4.71 at 35°C and 3.51 at 55°C, a point we go through on our Ecodan page. A system designed to run at 55°C because nobody wanted to change the radiators is a system you have pushed towards the losing end of the table on purpose.

What each one costs a year in an average gas household

Ofgem cut its typical gas consumption figure on 1 July 2026, and almost every comparison online is still using the old one. Table 1 of Ofgem's Review of typical domestic consumption values: decision sets the 2026 values for gas at 6,000 kWh a year for a low user, 9,500 kWh for a medium user and 14,000 kWh for a high user. The 2023 values it replaced were 7,500, 11,500 and 17,000. If you see an annual gas bill built on 11,500 kWh, it is 21% out of date before any price is applied.

Take the medium figure and run it through the current cap. A household burning 9,500 kWh of gas pays £757 in gas units plus £108 in gas standing charges, which is £865 a year for gas whatever else happens. At a boiler seasonal efficiency of 85%, those 9,500 kWh deliver 8,075 kWh of heat into the house. Here is what the same heat costs from a heat pump at today's electricity rate:

Two honest caveats on that table, because they move the numbers. Ofgem's consumption value is total gas use, so a home that also cooks with gas is not converting all 9,500 kWh into space heating and hot water. And the comparison assumes you stop paying the gas standing charge, which only happens if you have the supply disconnected rather than left capped and billed. Keep the gas connection for a hob and the saving at an efficiency of 2.5 disappears entirely.

Disconnecting the gas is worth more than most installers mention

The gas standing charge is 29.68p a day, which is £108 a year for burning nothing at all. That changes the break-even figure rather than just the saving: against the full £865 gas bill, a heat pump breaks even at a seasonal efficiency of 2.46, against 2.81 if you keep the gas on for cooking and only compare unit rates. The Energy Saving Trust makes the same point on its air source heat pump page, that if you are able to disconnect the gas once the heat pump is in, you save more because you are no longer paying the gas standing charge.

One thing to watch in the other direction. There is currently no VAT on domestic electricity in Great Britain from 1 October 2026 to 31 March 2027, while gas still carries 5%, and Ofgem flags on its own rates page that costs across those periods cannot be compared directly. Today's 3.30 ratio is flattered by that. When electricity VAT returns on 1 April 2027 the electricity side gets worse and every break-even figure above rises with it, which is why we track the underlying number on our page on the cost of electricity per kWh in the UK rather than hard-coding a saving.

Upfront, the grant has closed the gap to about £1,000 in England and Wales

The Energy Saving Trust puts a typical air source heat pump installation at around £12,000, and a gas boiler replacement at an average of £3,500 in Great Britain. Its boiler figure covers replacing a G-rated gas boiler with an A-rated one including thermostatic radiator valves, and it was last reviewed on 20 May 2026. The heat pump page was last reviewed on 23 September 2026.

Put that £1,000 difference next to the running cost table and the arithmetic becomes blunt. At a seasonal efficiency of 3.0 and the gas disconnected, the extra £1,000 comes back in about six and a half years. At 3.5 it comes back in four. At 2.5 it never does, because the £15 a year it saves is inside the noise of a cold winter. A payback calculation on a heat pump is a bet on the design quality of one specific installation, not on the technology.

The full breakdown of what sits inside that £12,000, including what changes off the gas grid, is on our UK heat pump cost guide.

The grant amounts, verbatim from gov.uk

The Boiler Upgrade Scheme is open to people in England and Wales only, and pays a fixed amount towards replacing a fossil fuel heating system. As published on gov.uk and read on 12 October 2026:

• £7,500 towards an air source heat pump, described there as an air-to-water heat pump
• £7,500 towards a ground source heat pump, including water source and shared ground loops
• £5,000 towards a biomass boiler, and £2,500 towards an air-to-air heat pump
• An additional £1,500 until March 2027 for a property heated by oil or LPG with no mains gas connection, which Ofgem states as a combined £9,000

One grant per property, and nothing at all for a hybrid system combining a gas boiler with a heat pump. You do not apply yourself: gov.uk's instruction is to contact suitable MCS certified installers for quotes, and the installer applies to Ofgem on your behalf, with the grant taken off the amount you pay and shown on the quotation and invoice. Note that the £1,500 uplift carries its own deadline, so a page quoting a bare £9,000 after March 2027 will be wrong while the £7,500 beside it stays right. There is no published closing date for the scheme itself on either the gov.uk or Ofgem consumer page, so treat anyone who gives you one as guessing.

The two installations are not regulated the same way, and the VAT is not the same either

A gas boiler replacement in England has to meet a minimum product efficiency of 92% ErP, and a heat pump installation has to be MCS certified to get the grant. The boiler standard comes from Boiler Plus, which applies whenever a boiler goes into an existing heating system anywhere in England. The government's own FAQ on it is specific about how the test works: the requirement applies to the boiler as an individual product, so a boiler below 92% ErP does not comply even if the system label is brought up to 92% by other components. A gas combination boiler also needs one extra efficiency measure from a list of four, being flue gas heat recovery, weather compensation, load compensation, or smart controls with automation and optimisation.

Two things follow for anyone comparing quotes. A modern replacement boiler is a better machine than the one it replaces, so the running cost you are comparing against is the new boiler's, not your current 15-year-old one's. And 92% ErP is a product label measured in a laboratory, not what a real system delivers across a winter with a 70°C flow temperature and no weather compensation, which is why the table above runs from 80% upwards.

On tax, HMRC's Notice 708/6 zero-rates the installation of a defined list of energy-saving materials until 31 March 2027, and air source and ground source heat pumps are on that list, with air source qualifying only where the unit is permanently fixed. From 1 April 2027 these supplies revert to the reduced rate of 5%. Energy-efficient boilers are not on the list and are standard-rated, unless the installation is grant-funded, in which case the 5% reduced rate applies. The same zero rate is what makes the sums work on VAT on solar panels, and it ends on the same date for both.

Scotland and Northern Ireland change the answer

The Boiler Upgrade Scheme does not exist outside England and Wales. In Scotland, Home Energy Scotland offers grant funding of up to £7,500 for heating systems such as heat pumps and heat network connections, with an additional £7,500 available as an optional interest-free loan, and a rural uplift on top for eligible households. It is not means-tested. In Northern Ireland, gov.uk states plainly that the Boiler Replacement Scheme is now closed, so the £12,000 is the number a Northern Irish household is working with, and the running-cost comparison is different again because the price cap covers England, Scotland and Wales only.

What actually decides which side of break-even your house lands on

Four things, and only one of them is on the quote. In rough order of how much they move the efficiency figure:

• Design flow temperature. Every 10°C you can take off it is worth a large slice of efficiency. It is the single number to ask for in writing.
• Emitter sizing. Flow temperature is set by the worst performing room in the house, so one undersized radiator taxes every other room's efficiency.
• Heat loss, as surveyed. A room-by-room calculation is what the design hangs on. An installer who sizes from floor area and a rule of thumb is guessing with your money.
• How it is run. Heat pumps are efficient held at a steady low temperature and inefficient in the short hard bursts a gas boiler tolerates. Keeping the gas boiler's timer habits is a common way to land below break-even.

The Energy Saving Trust's own framing of the outcome is worth quoting, because it is more honest than most sales material: on standard electricity tariffs, where electricity is nearly four times more expensive than gas, heat pumps can cost slightly more to run than new gas or oil boilers, while switching to a heat pump time-of-use tariff can reduce running costs enough that a heat pump costs less to run than a gas boiler. Both halves of that sentence are true, and which half applies to you is decided after the survey, not before it.

So which should you buy?

If your boiler has failed this week, your radiators are small, and you have no cylinder space, a new gas boiler is the rational purchase and there is no point pretending otherwise. A heat pump bought in a hurry is the one that lands at an efficiency of 2.5.

If you have a few months, radiators that are already generous or easy to change, somewhere for a cylinder, and you are in England, Wales or Scotland where the grant applies, the case is strong: about £1,000 more than a boiler on the day, a design that can reach an efficiency above three, and the gas standing charge gone. Add solar panels or a home battery later and the electricity side of the sum gets cheaper rather than dearer, which is not something a gas boiler can do. Our guide to Vaillant heat pumps covers what the equipment side of a quote should look like.

Whichever way you are leaning, the Energy Saving Trust's advice on both its boiler and heat pump pages is the same and it is right: get at least three quotes from certified installers, MCS for a heat pump and Gas Safe registered for gas. Get a Quote and we will pass your details to MCS-certified installers covering your postcode. The form takes about a minute, and the installer will want to survey the house before any price is firm.

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