Upfront Installation Costs
- Gas boiler replacement: £2,500–£4,500
- Air source heat pump (before grant): £12,000–£18,000
- ASHP after £7,500 BUS grant: £4,500–£10,500
Annual Running Costs
Based on a 3-bedroom semi-detached home (12,000 kWh annual heat demand):
- Gas boiler (gas at 7p/kWh, 90% efficiency): £933/year
- Heat pump (CoP 3.0, electricity at 24p/kWh): £960/year
- Heat pump (CoP 3.5, smart tariff at 17p/kWh): £583/year
Annual Servicing Costs
- Gas boiler annual service: £80–£120
- Heat pump annual service: £100–£200
Typical Repair Costs
- Gas boiler major repair (heat exchanger): £400–£800
- Gas boiler replacement every 12–15 years: £2,500–£4,500
- Heat pump major repair (compressor): £1,000–£2,500
- Heat pump lifespan 20+ years with servicing
15-Year Total Cost Comparison
Gas boiler: £4,000 install + £14,000 running + £1,800 service + £3,500 mid-life replacement = ~£23,300
Heat pump (with grant): £8,000 install + £11,700 running (smart tariff) + £2,250 service = ~£21,950
The lifetime costs are comparable, with heat pumps pulling ahead when on smart tariffs — and substantially ahead when replacing oil or LPG systems.
Sources: Ofgem price cap.
