Heat pump running cost for a 5+ bedroom detached house
A 5+ bedroom detached house uses roughly 24,000 kWh of heat a year. At the current Ofgem price cap an air source heat pump (SCOP 3.5) would cost about £1,790/yr to run, versus about £2,061/yr for mains gas. That is roughly £270 saved a year. A typical ~12kW system costs about £15,500, or £8,000 after the £7,500 grant, paying back in about 29.6 years.
Your standard rate. The tariff scenario is shown separately.
Efficiency. 3.5 is typical.
On a standard tariff (price cap)
electricity at 26.11p/kWh
£270 /yr saved
Heat pump £1,790/yr · payback 29.6 yrs
On a heat pump tariff (~15p/kWh)
cheap-rate electricity
£1,032 /yr saved
Heat pump £1,029/yr · payback 7.8 yrs
Heat pump tariffs (Octopus Cosy, EDF, Scottish Power) offered off-peak rates of about 14p to 15p/kWh in June 2026. The ~15p scenario assumes most heating runs in the cheap hours.
- Now: mains gas heating
- £2,061/yr
- Gas standing charge saved
- £106/yr
- Indicative system size
- ~12kW
- Install after grant
- £8,000
- CO₂ saved
- 3,461 kg/yr
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Estimate only. Real figures depend on your home, install and tariff. Prices: Ofgem cap, Jul-Sep 2026.