Heat Pump vs Gas Boiler Payback Calculator (UK)
Calculate UK heat pump installation payback vs continuing with gas boiler. Includes £7,500 BUS grant, electricity/gas tariffs, and 15-year running cost comparison.
Heat Pump vs Gas Boiler Guide (UK)
How Heat Pumps Work
An air source heat pump (ASHP) extracts heat from outside air using a refrigeration cycle and delivers it to your radiators or underfloor heating. Works even at -10°C outside — heat is moved, not generated. SCOP (Seasonal Coefficient of Performance): the average ratio of heat delivered to electricity used over a full UK heating season. Modern ASHPs: 2.8-3.5 SCOP typical. 3.5-4.0+ for ground source or well-designed installations. A SCOP of 3.0 means 1 kWh electricity delivers 3 kWh heat. Compare
Cost Comparison Reality (2026/27)
Per kWh of heat delivered (UK price cap 2026/27): gas: ~7p/kWh fuel cost. ÷ 90% efficiency = ~7.8p per kWh of heat. Heat pump: ~25p/kWh electricity. ÷ SCOP 3.0 = ~8.3p per kWh of heat. Basically the same on current tariffs. Where heat pumps win: heat pump tariffs (Octopus Cosy, British Gas Heat Pump tariff) offer 18-22p/kWh during off-peak heating windows. Bring heat pump cost per kWh of heat down to 6-7p — cheaper than gas. Heat pump tariffs typically have higher peak rates (e.g. Octopus Cosy:
Installation Cost and BUS Grant
Typical ASHP installation: £10,000-£16,000 unmodified. Includes: outdoor unit, indoor unit (or hydrobox), hot water cylinder, controls, installation labour, commissioning. Larger systems for poorly-insulated homes: £14,000-£20,000+. Boiler Upgrade Scheme (BUS): £7,500 grant for air source heat pump (was £5,000, increased October 2023). Available to homeowners and small landlords in England, Wales, Scotland. Net cost after grant: £2,500-£8,500 typical for ASHP. Versus £2,500-£4,500 for replacemen
Suitability Checklist
Heat pumps work well in: well-insulated homes (EPC C or better ideally — D acceptable if no major draughts). Homes with low-temperature heating systems (underfloor heating preferred; oversized radiators acceptable). Homes with outdoor space for unit (1m+ clearance, not in enclosed alcove). Homes with reliable electricity supply. Heat pumps work poorly in: poorly-insulated solid wall pre-1920 properties (need expensive insulation upgrades first). Homes with undersized radiators kept at high-tempe
Recommended for this calculator