This article contains affiliate links. We may earn a commission if you buy through our links, at no extra cost to you. Running-cost figures are from Energy Saving Trust and Ofgem’s published unit rates, and installer prices from Heatable and iHeat’s own pages, checked in August 2026 and subject to change. Last reviewed: August 2026.
An air source heat pump costs about the same to run as a new gas boiler if you stay on a standard electricity tariff, and it can come in cheaper on a dedicated heat-pump tariff. The catch is everything around the unit: the tariff you actually go on, how well insulated the house is, the efficiency the survey designs to, and whether the pump and radiators are sized for the heat loss. Get those right and it sits near gas or below it; get them wrong and it can cost more than the boiler it replaced.
Energy Saving Trust are blunt about it: most heat pumps on a flat-rate tariff cost the same or even a little more to run than an efficient gas boiler, and the saving only really appears once you switch to a heat-pump tariff, where they put the heating-bill saving at up to £330 a year. That’s the annual bill. What you pay to have the unit fitted is a separate question, covered in our air source heat pump cost guide, and if you’re weighing it against staying on gas, see heat pump vs boiler.
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Air source heat pump running cost: the short version
On a standard electricity tariff, Energy Saving Trust put a heat pump’s running cost around the same as a new gas boiler, and sometimes slightly more, because electricity costs several times more per unit than gas. The saving shows up when you move to a dedicated heat-pump or time-of-use tariff, where EST’s research finds up to £330 a year off the heating bill. The brands’ own figures run higher, iHeat advertise £500+ and Octopus quote around £200 on their Cosy tariff, but those are marketing on their own kit and assumptions. What actually decides your bill is the tariff, the insulation, the efficiency the survey designs to, and whether the unit is sized right.
What actually decides the running cost
There’s no single annual bill that fits every house. Four things move it: the electricity tariff, how leaky the fabric is, the seasonal efficiency (SCOP) the installed system actually hits, and whether the unit and radiators are sized for the heat loss. Miss any one and a heat pump that should sit near gas can end up costing more than the boiler it replaced.
Heatable put a well-designed air source heat pump in a fully insulated, leak-free home at around 300% efficient, and iHeat say heat pumps are up to four times more efficient than a traditional boiler. Those are design results in a good house. A Victorian terrace on tired radiators and a standard-rate tariff is a different job, which is exactly what the heat-loss survey is there to catch.
Flow temperature is the boring bit that decides the bill. Heat pumps like lower flow temperatures than a combi, and bigger emitters, or underfloor heating, let you drop that temperature and lift the SCOP. Smaller radiators force the unit to work harder and push the cost up. Heatable are blunt on their heat-pump page that old, leaky homes with tired radiators may need upgrades before a heat pump works well.
How much a heat pump costs to run versus gas
On standard electricity tariffs, where electricity is several times more expensive per unit than gas, Energy Saving Trust say a heat pump can cost slightly more to run than a new gas or oil boiler, about the same as a new gas boiler at current prices, cheaper if you’re replacing an older boiler, and cheaper still on a heat-pump time-of-use tariff. The useful comparison is the cost of a unit of actual heat, which is the unit rate divided by the efficiency:
| How you make the heat | Cost per kWh of useful heat |
|---|---|
| Gas boiler at 90% | About 8.1p |
| Gas boiler at 85% (the efficiency Octopus compare against) | About 8.6p |
| Heat pump at SCOP 3.0 (Heatable’s well-insulated case) | About 8.7p |
| Heat pump at SCOP 3.5 | About 7.5p |
| Heat pump at SCOP 4.0 (iHeat’s “up to 4x”) | About 6.5p |
That’s arithmetic on Ofgem’s 1 July to 30 September 2026 Direct Debit rates (26.11p per kWh for electricity, 7.33p for gas, both including 5% VAT). It’s a per-unit comparison, not an annual bill. Read it and the picture is clear: at a 300% SCOP on the standard cap you’re a fraction above a 90% gas boiler; at SCOP 3.5 you’re under it; at a poor SCOP in a leaky house you go the other way. The survey, the emitters and the tariff decide which row you actually live on.
The tariff is the lever that matters most. EST’s own research on matching heat pumps to the right tariff found that switching from gas without changing tariff often means little or no saving, while a heat-pump-appropriate tariff (a dedicated heat-pump tariff, or a dynamic one that changes through the day) can save up to £330 a year on heating bills. If you disconnect the gas supply entirely, including for cooking, EST add roughly £105 a year in saved standing charge on July 2026 prices, which lines up with Ofgem’s current gas standing charge of 29.04p a day, about £106 a year.
What the brand savings claims actually mean
iHeat’s heat-pump page advertises “£500+” potential annual savings, and their FAQ puts typical bill savings versus gas at £200 to £600 a year, on the same page as their “up to 4x more efficient” line. Octopus say Cosy heat pump customers on the Cosy Octopus tariff saved an average of £200 over the year to 1 July 2026 against a gas boiler running at 85% on their standard variable tariff, with the small print on the same article putting it at £224.
Both are the companies’ own figures, measured on their own kit, tariffs and assumptions, so treat them as a best case rather than your bill. Energy Saving Trust’s up-to-£330 is the more neutral number, and it still depends on you actually switching tariff. For context on Octopus’s median price and Cosy range, our Octopus heat pump review weighs the Cosy up as a competitor.
Running cost versus what it costs to fit
Running cost is the annual bill; the fitted price is a separate number. Heatable’s FAQ puts a typical installation at £7,000 to £13,000 before the grant, and iHeat’s live catalogue is the Alpha Hydro at £10,595 (from £221 a month), the Vaillant aroTHERM Plus at £11,495 (from £239) and the Worcester 5800i at £11,995 (from £250), all including VAT before the grant. Heatable’s paid step is a £240 heat-loss survey, deducted if they install, and they don’t need a named model on the quote form. The full breakdown is in our air source heat pump cost guide.
The Boiler Upgrade Scheme closes the install gap, not the running-cost gap. It takes £7,500 off an eligible air-to-water heat pump in England and Wales, or £9,000 if you’re off-gas replacing oil or LPG from 21 July 2026 to 31 March 2027, and the installer claims it. Full rules are in our Boiler Upgrade Scheme guide, how to spread the balance is on heat pump finance, and if a new combi is still on the table, see heat pump vs boiler.
Heatable first, iHeat for a named model or 0%
Both are MCS-certified and both apply for the £7,500 grant, but the survey is what tells you whether the running cost will sit near gas or above it. Heatable is the first quote for most homes; iHeat is the second number, or the first if you already want Vaillant aroTHERM Plus, Alpha Hydro or Worcester 5800i.
- Instant estimate, then a £240 heat-loss survey
- £240 refunded if they install
- Around 300% efficient in a well-insulated home, on their page
- BUS paperwork handled, MCS + Which?
- Alpha Hydro, Vaillant aroTHERM Plus or Worcester 5800i
- 0% APR on heat pumps, 12-month BNPL
- Their £500+ saving figure is a best case, not a guarantee
- BUS paperwork handled, MCS engineers
Who a running-cost saving is actually for
The honest read: a heat pump is a running-cost win if the house can take a low flow temperature, you’ll switch off a standard flat-rate tariff, and you’re replacing an older or oil/LPG boiler rather than a brand-new 90% combi. It’s a running-cost shrug, or a loss, if you stay on the cap rate in a leaky house with tired radiators and hope the grant magics the bill down.
This is for you if
- The house is decently insulated, or you’ll upgrade the fabric first
- You’ll move onto a heat-pump or dynamic tariff
- You can wait for a heat-loss survey rather than heat this week
- You’re off-gas on oil or LPG, where the gap versus fossil is wider
Look elsewhere if
- The boiler is dead and you need heat this week
- You have a combi and no space for a cylinder
- You’ll stay on a standard tariff and expect a big cut
- You won’t let the survey change radiators or flow temperature
If any of those “look elsewhere” lines are true, a replacement combi is still the cheaper, faster job, and our new boiler cost guide covers that band.
How to buy
- Most homes: start with Heatable for a free estimate, then the £240 survey deducted if they install.
- Named brand (Vaillant, Alpha, Worcester) or 0% APR: add iHeat, whose catalogue is the public price list.
- Running cost: ask both what SCOP they’re designing to and which tariff they assume, and treat any brand savings figure as a best case rather than your bill.
- Off-gas on oil or LPG: ask both to price the £9,000 grant uplift, not only the £7,500.
- Scotland or Northern Ireland: the Boiler Upgrade Scheme doesn’t apply, though the running-cost logic still does.
Frequently asked questions about heat pump running costs
How much does an air source heat pump cost to run in the UK?
Energy Saving Trust put running costs around the same as a new gas boiler on a standard electricity tariff, and sometimes slightly more. Their research says a heat-pump-appropriate tariff can save up to £330 a year on heating bills. There’s no single reliable annual figure, because it depends on your tariff, insulation, SCOP and sizing.
How much does a heat pump cost to run versus a gas boiler?
On Ofgem’s July to September 2026 Direct Debit cap (26.11p electricity, 7.33p gas), a 90% gas boiler costs about 8.1p per kWh of useful heat. A heat pump at SCOP 3.0 costs about 8.7p, at SCOP 3.5 about 7.5p, and at SCOP 4.0 about 6.5p. Your survey and tariff decide which figure you get.
Is Octopus’s £200 running-cost claim real?
It’s their Cosy-tariff figure: Octopus say Cosy customers on the Cosy Octopus tariff saved an average of £200 over the year to 1 July 2026 against an 85% gas boiler on their standard variable tariff, with the small print putting it at £224. It’s measured on their own kit and tariff, so treat it as a best case.
Will a leaky house cost more to run?
Yes. Higher heat loss means a larger unit, higher flow temperatures and a worse SCOP. Heatable say old, leaky homes with tired radiators may need upgrades before a heat pump works well. The grant no longer treats loft and cavity recommendations as a hard gate, but a poorly insulated house still costs more to run.
Does the grant cut my running cost?
No. The Boiler Upgrade Scheme knocks £7,500 (£9,000 off-gas oil or LPG to 31 March 2027) off the install invoice in England and Wales. It doesn’t change the unit rate you pay for electricity. Running cost comes down to tariff, insulation, SCOP and sizing.
Who should I quote?
Heatable first via the heat-pump link, iHeat second. Heatable publish a typical £7,000 to £13,000 band and a £240 survey deducted if they install; iHeat publish named packages and 0% APR. HomeBoiler is not a credit broker, lender or installer.