Heat Pump vs Gas Boiler Calculator
Side-by-side 15-year total cost of ownership for your home. Includes install, BUS grant, running costs, maintenance, and the gas boiler replacement most people forget in year 10.
Updated 27 May 2026
15-year cost · heat pump vs gas, head-to-head
Full TCO including install, fuel, maintenance, and the gas boiler replacement most articles forget at year 10.
Quick answer: After the £7,500 BUS grant and on Octopus Cosy tariff, a typical UK 3-bed semi pays £14,500 over 15 years for a heat pump vs £18,500 for a gas boiler (including the replacement boiler at year 10). Heat pump saves around £4,000 over 15 years. Without the grant, gas wins by ~£3,500. The grant is the decisive factor.
Your home
15-year total cost difference
£4,000 saved
heat pump wins
Heat Pump 15-yr
£14,500
Gas Boiler 15-yr
£18,500
Includes install, fuel, annual service. Excludes radiator upgrades, DNO costs.
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How the comparison is built
The honest 15-year comparison includes every cost most "savings" articles skip:
| Cost item | Heat pump | Gas boiler |
|---|---|---|
| Install | £13,500 | £3,000 |
| Less BUS grant | −£7,500 | — |
| Net install | £6,000 | £3,000 |
| Fuel year 1 | £705 | £985 |
| Fuel × 15 yrs (constant prices) | £10,575 | £14,775 |
| Annual service × 15 | £1,200 (£80/yr) | £1,350 (£90/yr) |
| Year-10 replacement | £0 (still under warranty) | £3,200 (new boiler) |
| 15-year TOTAL | £17,775 | £22,325 |
The default "save £4,000" headline includes that year-10 gas boiler replacement most consumer comparisons forget. Average UK boiler life is 12–13 years on modern condensing models — so over a 15-year window, you will pay for almost two boilers vs one heat pump that's still going strong at year 15.
What changes the answer
Heat pump wins by MORE if:
- You qualify for the £7,500 BUS grant
- You're on Octopus Cosy or Go (knocks ~£200/yr off running cost)
- Your install gets SCOP 3.3+ (modern install with sized radiators)
- Gas prices rise above the 4%/yr OBR baseline (very likely)
- Your gas boiler is at end-of-life anyway (avoid the £3,000 replacement)
Gas boiler wins if:
- You're not eligible for BUS (no EPC, hybrid system, etc.)
- Your current boiler is under 5 years old and working perfectly
- You're on the standard cap and unwilling to switch to Cosy
- Your home is hard-to-heat solid-wall with no insulation budget
- You're moving in under 5 years (you won't recoup install)
The decision framework
Ignore the running cost obsession for a moment. The honest decision tree is:
- Is your boiler about to fail? If yes → heat pump almost always wins.
- Do you qualify for the £7,500 grant? If yes → heat pump wins more.
- Will you stay 10+ years? If yes → heat pump wins.
- Can you switch to Octopus Cosy? If yes → heat pump wins.
- Is your home reasonably insulated (EPC C or better)? If yes → heat pump wins comfortably.
Score 4 or 5 yeses? Get heat pump quotes today. Score 2 or fewer? Replace the gas boiler when it dies, and revisit in 3 years when grants and tariffs have moved.
Frequently asked questions
Is a heat pump cheaper than a gas boiler over 15 years?
Yes for most UK homes that qualify for the £7,500 BUS grant. A typical 3-bed semi on Octopus Cosy costs £17,775 over 15 years with a heat pump vs £22,325 with gas (including the gas boiler replacement at year 10). The grant tips the maths decisively. Without the grant, gas wins by ~£3,500 over 15 years.
Should I replace my gas boiler with a heat pump now?
Yes if your boiler is over 10 years old and you qualify for the £7,500 grant. The grant won't last forever, and gas prices are forecast to rise 4–6% annually (OBR). Wait if your boiler is under 5 years old and working well — the maths swings against early replacement because you'd lose the value of the existing boiler.
What's the real annual running cost difference?
On Octopus Cosy with a SCOP 3.0 heat pump, the typical 3-bed semi saves £200–£350 per year vs a modern gas boiler. On the standard cap, savings shrink to £0–£100/yr. The tariff matters more than people realise — Cosy is the difference between a clear win and break-even.
Does the comparison change if gas prices rise?
Yes, in the heat pump's favour. The OBR projects UK gas to rise 4–6% per year and wholesale electricity to fall 2–3% per year as renewables grow. By year 15, the running-cost gap typically doubles vs the year-1 figure. The calculator above uses constant prices for simplicity — real numbers will be more favourable to heat pumps.
What about hydrogen-ready boilers — should I wait?
No. The UK government dropped the 2026 hydrogen heating decision indefinitely. The "hydrogen-ready" sticker on new boilers is meaningless — there's no domestic hydrogen network, no plan to build one, and no cost-competitive route to green hydrogen for home heating. Don't wait for a technology that won't arrive.
Heat pump or just keep replacing my gas boiler forever?
The "forever gas boiler" path costs ~£28,000–£32,000 over 30 years (3 boilers + 30 years of fuel + rising gas prices + standing charge). The "two heat pumps over 30 years" path costs ~£24,000–£28,000 with grants. The crossover happens around year 18. If you're under 60, heat pump wins. If you're over 75 and don't expect to outlive the current boiler, gas is fine.