Heat pump running cost for a 3-bedroom flat / apartment
A 3-bedroom flat / apartment uses roughly 9,000 kWh of heat a year. At the current Ofgem price cap an air source heat pump (SCOP 3.5) would cost about £671/yr to run, versus about £839/yr for mains gas. That is roughly £168 saved a year. A typical ~5kW system costs about £10,500, or £3,000 after the £7,500 grant, paying back in about 17.9 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
£168 /yr saved
Heat pump £671/yr · payback 17.9 yrs
On a heat pump tariff (~15p/kWh)
cheap-rate electricity
£453 /yr saved
Heat pump £386/yr · payback 6.6 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
- £839/yr
- Gas standing charge saved
- £106/yr
- Indicative system size
- ~5kW
- Install after grant
- £3,000
- CO₂ saved
- 1,298 kg/yr
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Estimate only. Real figures depend on your home, install and tariff. Prices: Ofgem cap, Jul-Sep 2026.