Heat Pump Savings Calculator

A heat pump's headline efficiency is its COP, the coefficient of performance. A COP of 3 means three units of heat for every one unit of electricity. Modern air source units in well-insulated UK homes hit a COP of 3.5 over a full heating season. In a draughty Victorian terrace with single glazing, the same kit struggles to manage 2.8 because the radiators have to run hotter to fight the heat loss.

The calculator builds this in directly: a 'good' insulation rating uses a COP of 3.5, 'average' uses 3.2 and 'poor' uses 2.8. That gap is roughly £200 to £400 a year in running cost on a £1,500 baseline heating bill. Spending £2,000 on loft and cavity wall insulation before fitting a heat pump usually pays back faster than the heat pump itself.

An air source heat pump installed in a semi-detached UK house typically costs around £10,000 fitted. The Boiler Upgrade Scheme grant of £7,500 (current 2026/27 figure) drops the net cost to £2,500. Against a £1,500 gas bill, the annual saving comes out to roughly £580 once you account for the COP, giving a payback of about 4.3 years on the net cost. Without the grant, that stretches to closer to 17 years.

Two caveats. First, the BUS grant is funded yearly and demand has occasionally exceeded supply; the calculator assumes you secure it. Second, electricity prices and gas prices move independently. If gas drops 30 percent or electricity climbs 30 percent, the saving narrows. Pair a heat pump with solar PV and a time-of-use tariff and the running cost drops sharply because the heat pump leans on cheap (or free) electricity.