Heat Pump vs Gas Boiler Payback Calculator (UK)

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. Compared to a gas boiler's efficiency of roughly 90%, even a modest SCOP of 3.0 delivers noticeably more heat per unit of energy input.

What should I know about 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 — for example Octopus Cosy, which offers cheaper rates specifically during typical heat pump running hours, in exchange for a higher rate at other times.

What's the key thing to understand about 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 a replacement gas boiler, meaning the upfront cost gap after the grant is often smaller than people expect.

What do I need to know about 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-temperature settings, since heat pumps work best with larger radiators or underfloor heating running at lower flow temperatures than a gas boiler typically uses.