Heat Pump vs Gas Boiler 2026: Real-Cost Comparison on a 3-Bed Semi
After the Boiler Upgrade Scheme grant (£7,500), an air source heat pump costs £1,000–£5,000 to install. Running costs are roughly comparable to a gas boiler in a well-insulated home — but can be significantly higher in a poorly insulated one.
The Key Comparison at a Glance
| Air Source Heat Pump | Gas Condensing Boiler | |
|---|---|---|
| Install cost (before grant) | £8,000–£13,000 | £2,000–£4,500 |
| BUS grant | −£7,500 | None |
| Net install cost | £500–£5,500 | £2,000–£4,500 |
| Running cost (well insulated) | 6–8p/kWh heat | 6p/kWh heat |
| Running cost (average insulation) | 8–10p/kWh heat | 6p/kWh heat |
| Running cost (poor insulation) | 12–16p/kWh heat | 6–8p/kWh heat |
| CO₂ emissions | Low (varies with grid mix) | ~200g CO₂/kWh heat |
| Maintenance | ~£150–£250/year | ~£80–£150/year |
| Lifespan | 20–25 years | 12–15 years |
A Typical 3-Bed Semi: Annual Heating Costs
Assumptions: 3-bed semi-detached, EPC band D (average UK efficiency). Annual heat demand approximately 12,000–15,000 kWh.
| Heating System | Annual Heat Demand | Unit Rate | Annual Fuel Cost |
|---|---|---|---|
| Gas boiler (90% efficiency) | 15,000 kWh (gas input) | 6p/kWh | £900 |
| Heat pump, CoP 2.5 (poor insulation) | 6,000 kWh electricity | 24p/kWh | £1,440 |
| Heat pump, CoP 3.0 (average insulation) | 4,500 kWh electricity | 24p/kWh | £1,080 |
| Heat pump, CoP 3.5 (good insulation) | 3,860 kWh electricity | 24p/kWh | £926 |
| Heat pump, CoP 4.0 (well insulated + UFH) | 3,375 kWh electricity | 24p/kWh | £810 |
Gas at 6p/kWh, electricity at 24p/kWh (Ofgem price cap April 2026 rates, typical).
At CoP 3.0 (realistic for average UK home, radiators not upgraded), the heat pump costs approximately £180/year more to run than a gas boiler. At CoP 4.0 (well-insulated home, underfloor heating or larger radiators), it costs approximately £90/year less.
The CoP (Coefficient of Performance) Explained
CoP measures how much heat energy a heat pump produces for each unit of electricity consumed.
| CoP | Meaning | Typical scenario |
|---|---|---|
| 2.0 | 1 kWh electricity → 2 kWh heat | Cold weather, undersized heat pump, poor insulation |
| 2.5 | 1 kWh electricity → 2.5 kWh heat | Poor–average insulation, standard radiators |
| 3.0 | 1 kWh electricity → 3.0 kWh heat | Average insulation, some radiator upgrades |
| 3.5 | 1 kWh electricity → 3.5 kWh heat | Good insulation, upgraded radiators |
| 4.0 | 1 kWh electricity → 4.0 kWh heat | Well insulated, low-temperature UFH, modern home |
Heat pumps work by extracting heat from outdoor air and concentrating it. They are more efficient when:
- The temperature difference between outside air and the target flow temperature is small
- The home is well insulated (requires lower flow temperatures)
- The emitters (radiators or UFH) are sized for lower temperature output
Upfront Cost vs Lifetime Cost
Scenario: Compare a heat pump vs a gas boiler replacement on a 20-year horizon.
| Heat Pump (ASHP) | Gas Boiler | |
|---|---|---|
| Install (net of grant) | £3,500 | £3,000 |
| Annual running cost (avg UK home, CoP 3.0) | £1,080 | £900 |
| Annual maintenance | £200 | £120 |
| Replacement cost (year 12–15 for boiler) | £0 (HP lasts 20–25 yrs) | £3,000 (new boiler at year 13) |
| 20-year total | £26,100 | £30,600 |
Over 20 years, the heat pump comes out approximately £4,500 cheaper in this scenario — despite higher running costs — because:
- The upfront cost difference is small after the grant
- The heat pump doesn't need replacing mid-period
- Running costs are close (not dramatically higher)
The gap widens further if:
- Electricity prices fall relative to gas (likely as grid decarbonises)
- The home's insulation is improved
- Carbon pricing on gas increases bills
When a Heat Pump Is Worth It
A heat pump is likely to be worthwhile if:
- Your home is EPC band C or better — Good insulation means the heat pump operates at higher CoP, keeping running costs low
- You have or plan underfloor heating — UFH runs at much lower flow temperatures (30–40°C vs 60–70°C for radiators), maximising CoP
- You are in a rural area or off-grid — Homes on oil or LPG heating (much more expensive than gas) see significant savings switching to heat pumps even at lower CoP
- You plan to stay in the property 10+ years — Amortises the install cost over a long period
- You care about carbon emissions — Heat pumps on the UK grid are already significantly lower carbon than gas boilers and will improve further as renewable generation grows
A heat pump is probably not the right choice if:
- Your home is EPC E or below without planned insulation upgrades
- You plan to sell in the next few years
- You cannot tolerate higher running costs even temporarily
- Your gas supply is reliable and cheap (city centre location)
The Boiler Upgrade Scheme (BUS) — 2025/26
| Air Source Heat Pump | Ground Source Heat Pump | |
|---|---|---|
| BUS Grant | £7,500 | £7,500 |
| Availability | England and Wales | England and Wales |
| Installer requirement | MCS certified | MCS certified |
| EPC requirement | Valid EPC, under 10 years | Valid EPC, under 10 years |
| Insulation requirement | Outstanding loft/cavity recs resolved | Outstanding loft/cavity recs resolved |
The BUS grant is in the form of a reduction in upfront cost — your installer applies and you pay the net amount. Funding is allocated on a first-come, first-served basis within each year. Check the Ofgem BUS page or your installer for current availability.
Other Costs to Factor In
| Item | Likely cost | Notes |
|---|---|---|
| Hot water cylinder | £500–£1,000 | Heat pumps need a cylinder; many homes with combi boilers don't have one |
| Radiator upgrades | £150–£400 per radiator | May need upsizing to work at lower flow temps |
| Electrical upgrade | £500–£1,500 | Some homes need consumer unit upgrade or new circuit |
| Insulation (top-up) | £500–£4,000 | Often needed to maximise CoP and may be required for BUS eligibility |
Total installed cost including ancillary works can be £10,000–£20,000 before grant in some cases. Subtract £7,500 grant and the net outlay could be £2,500–£12,500 depending on property.
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