Heat pump running costs: the assumptions that change the answer
Compare heat demand, seasonal performance and electricity price without relying on a one-size-fits-all savings claim.
Reviewed 5 August 2026 · CoolCompare Editorial
Start with useful heat demand
A heat pump bill cannot be estimated from floor area or appliance output alone. Begin with the useful heat the building needs over a year. A recent heating assessment, fuel history adjusted for boiler efficiency, or a competent heat-loss model provides a stronger starting point than a generic household average.
Fabric condition changes that demand. Loft insulation, draught reduction and sensible controls can reduce heat required, while extensions, long heating schedules and high hot-water use can increase it. Record the demand assumption before comparing systems.
Use seasonal performance—not brochure COP
COP is a performance ratio at a stated test point. Annual electricity use is better modelled with a seasonal coefficient of performance, or SCOP, that reflects outdoor conditions, water temperatures, defrost and the system design.
Divide annual useful heat by the design SCOP to estimate electricity. A 12,000kWh heat demand at SCOP 3.2 implies about 3,750kWh before considering backup heat or other differences. Test a cautious and an optimistic SCOP rather than presenting one result as certain.
Compare tariffs and systems fairly
Multiply estimated electricity by the tariff rate that will actually apply. If a time-of-use tariff is proposed, model the proportion that can realistically move; a heat pump must still serve the home outside cheap windows.
For a boiler comparison, divide useful heat by assumed boiler efficiency before applying the gas rate. Keep standing charges, maintenance and capital costs separate so the comparison does not mix annual energy with ownership cost.