Heat pump vs gas boiler: an honest comparison
Heat pumps are not strictly better than gas boilers, and gas boilers are not strictly cheaper. It depends on your property, your tariff and your time horizon. This guide compares them on the criteria that actually matter.
At-a-glance
| Criterion | Gas boiler | Heat pump (ASHP) |
|---|---|---|
| Install cost | £2,500 – £4,500 | £10,000 – £14,000 (gross), £2,500 – £6,500 after BUS |
| Annual running cost (3-bed semi, 2026 cap) | £1,100 – £1,500 | £900 – £1,400 |
| Lifespan | 10–15 years | 15–20 years |
| Servicing | £90 / year + boiler cover | £150 – £250 / year |
| Outdoor space needed | None | 1.5 m clearance from outdoor unit |
| Radiator upgrades typical? | Rare | Often 1–3 needed |
| Carbon (kg CO₂e / year, 3-bed) | ~2,200 kg | ~450 kg (and falling as grid decarbonises) |
Where heat pumps win
- Lower carbon, today. A UK ASHP at SCOP 3.5 emits roughly 80% less CO₂ than a gas boiler. The gap widens every year as the grid decarbonises.
- Running costs, with the right tariff. On a heat-pump-friendly time-of-use tariff (Octopus Cosy, EDF, etc.) the running cost gap can swing 20–30% in the heat pump's favour. On the standard variable rate, gas is usually slightly cheaper to run.
- Lifespan. Heat pumps typically last 15–20 years, gas boilers 10–15. Over a 20-year horizon you may replace a gas boiler twice.
- Future-proofing. Gas boiler bans in new-build came in for 2025. Government direction of travel is toward low-carbon heat; expect gas-related running costs and standing charges to keep rising.
- Cooling. Most modern ASHPs can run in reverse for summer cooling. A gas boiler cannot.
Where gas boilers still win
- Up-front cost. Even after BUS, a heat pump install costs more than a like-for-like boiler swap.
- Simplicity of retrofit. Replacing one gas boiler with another is a 1-day job. A heat pump install is 2–5 days plus design.
- Old, leaky properties. A heat pump can heat a Victorian terrace with single-glazed windows, but it needs careful sizing and you'll spend more on radiators. A gas boiler can over-pump heat into a leaky house at the cost of bills.
- Hot taps right now. A combi gas boiler delivers instant hot water from the tap. A heat pump needs a stored cylinder.
The retrofit question
For a well-insulated property, a heat pump is almost always the better long-term choice. For a draughty, leaky property, the right order is: insulation first, then heat pump. The Boiler Upgrade Scheme actually requires recent EPC recommendations on loft and cavity wall insulation to be implemented before you can claim.
15-year total cost of ownership
For a typical 3-bed semi in 2026, with current grant rates and a moderate gas/electric tariff:
| Gas boiler | ASHP | |
|---|---|---|
| Install (incl. one replacement at year 12 for gas) | £7,000 | £4,500 (after BUS) |
| Servicing × 15 years | £1,400 | £3,000 |
| Running costs × 15 years (rising 2% real) | £20,000 | £17,500 |
| Carbon cost (if priced at £100/tonne) | £3,300 | £700 |
| 15-year total | £31,700 | £25,700 |
Indicative only — your figures depend on property efficiency, tariff and grant changes. Source: 2026 install costs, current Ofgem cap (3-bed semi consumption averages from Ofgem), BUS rules.
When to choose what
Choose a heat pump if:
- Your property is reasonably well insulated, or you're willing to upgrade insulation first.
- You have outdoor space for the unit.
- Your 15-year horizon matters and you can use the BUS grant.
- You're willing to learn to use the system (lower flow temps, run it more steadily).
Choose a gas boiler if:
- You need a quick like-for-like replacement and can't accommodate a 2–5 day install.
- Your property is a heritage building with strict planning constraints on outdoor units.
- You are likely to move within 5 years and won't recover the up-front cost.
Ready to get heat pump quotes? Start by finding installers in your region, then read our questions to ask guide.