Heat Pump kWh Savings Calculator

The calculator compares your current annual heating cost against the projected cost of running an air source heat pump. It uses your current fuel type's unit rate and boiler efficiency to derive your heat demand in kWh, then applies a Seasonal Performance Factor (SPF) to calculate what an ASHP would cost to deliver the same heat output. SPF is adjusted for property age based on UK field trial data.

The base SPF of 2.8 comes from the UK Government's Electrification of Heat trial — the largest real-world dataset of UK heat pump installations (742 properties). This figure is adjusted upward for newer, better-insulated properties (2000+) and downward for older properties (pre-1940) where radiator upgrades may be needed for optimal performance.

Because gas is currently the UK's cheapest fossil fuel at ≈6.99p/kWh. An ASHP running on electricity at 27.69p/kWh divided by a SPF of 2.8 produces an effective heat cost of approximately 9.9p/kWh — more expensive than gas per unit of heat, though offset by the £9,000 BUS grant. For oil (≈9.5p/kWh at 85% efficiency = effective cost ≈11.2p/kWh) and LPG (≈14.2p/kWh effective), the ASHP is significantly cheaper to run.

Yes. The net installation cost displayed automatically deducts the £9,000 BUS grant from your entered installation cost. The payback period is calculated against this net figure. You must use an MCS-certified installer and hold a valid EPC to qualify for the grant.

Solar panels generate electricity during the day that can power your heat pump directly, reducing your reliance on grid electricity. The calculator applies a 15% effective electricity cost reduction when solar is selected, representing a typical contribution from a 4kWp system during the heating shoulder season (spring and autumn). The actual impact depends on your system size, orientation, and heating pattern.