Air Source Heat Pump Savings Calculator
Calculate the annual running costs and potential savings of switching from a gas boiler to an air source heat pump — including the Boiler Upgrade Scheme grant.
Air Source Heat Pump Guide
How Heat Pumps Work
An air source heat pump (ASHP) extracts heat from outside air and moves it inside — like a refrigerator working in reverse. For every 1 kWh of electricity used, a modern ASHP delivers 2.5–4 kWh of heat, giving a coefficient of performance (COP) of 2.5–4.0. At COP 3 and electricity at 24.5p/kWh, the effective heat cost is 24.5/3 = 8.2p/kWh, compared to gas at 5.5p/kWh ÷ 0.9 boiler efficiency = 6.1p/kWh. Currently, gas heating is often cheaper per unit but this gap is narrowing.
The Boiler Upgrade Scheme
The UK Government's Boiler Upgrade Scheme provides a £7,500 grant toward the purchase and installation of an air source heat pump (from April 2024 upwards). This significantly changes the financial case: a £12,000 installation becomes £4,500 net. Applications are made through the installer — not by the homeowner directly. The scheme requires an EPC (Energy Performance Certificate) rated D or below without a recommendation to add cavity wall or loft insulation unless it has already been done.
When Heat Pumps Work Best
Heat pumps work best with: underfloor heating or large, low-temperature radiators (optimised for 40–50°C flow rather than gas boilers' 60–80°C); good insulation (heat pumps work harder in poorly insulated homes, reducing efficiency); modern double or triple glazing; and a buffer tank for hot water. Properties with solid walls (no cavity insulation) and no underfloor heating typically see worse economics until they are insulated first. The Passivhaus-style of buildings (excellent insulation, mini
Financial Outlook
The electricity-to-gas price ratio matters enormously. At current UK prices (electricity ~24p, gas ~5.5p), the price ratio is approximately 4.4:1. For a heat pump to match gas on running costs, it needs a COP above 4.4 — achievable in mild weather but often not in deep winter when heat demand is highest and COP is lower. The case for heat pumps improves as: the electricity price ratio falls (more renewables reduce electricity cost), gas prices rise (North Sea depletion, import dependency), carbo
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