The Green Calculator Beta
Calculate my savings
Calculators
Solar CalculatorBattery Calculator Heat Pump CalculatorEV Charger Calculator Home Energy AuditEnergy Bill Optimiser Carbon FootprintAll calculators
Suppliers
RankingsSwitching The Big 6 Octopus EnergyBritish Gas E.ON NextOVO Energy EDF EnergyScottishPower Smaller providers Utility WarehouseGood Energy So EnergyEcotricity Fuse Energy100Green Outfox EnergyTruEnergy Home EnergyE
Technologies
Solar PanelsHome Batteries Heat PumpsEV Chargers Smart TariffsHome Insulation
Grants
Learn
Beginner GuidesComparisons Buying GuidesWorked ExamplesAll articles
NewsAbout Calculate my savings
♨️ Heat pump calculator

Would a heat pump cost less to run?

An air-source heat pump turns one unit of electricity into roughly three of heat. Whether that beats your boiler comes down to your heat demand, the unit's efficiency and your tariff. Here is the comparison, with the £7,500 grant included.

Delivered heat. A typical 3-bed uses 11,000 to 13,000 kWh; a well-insulated flat far less.
Seasonal performance. Well-designed systems on radiators reach 3.2 to 3.6; underfloor higher.
Heat-pump tariffs (such as Cosy Octopus) discount the hours a heat pump runs most.
Running cost change / year
−£40
vs your current heating
Current heating cost£930
Heat pump running cost£890
Electricity it uses3,530 kWh
Install cost after grant£4,000
Payback on the upfront cost—
CO₂e cut / yr1.1 t

Gas factor 0.183, electricity 0.207 kgCO₂e/kWh (DESNZ 2024). Install ~£11,500 before grant.

How this is worked out

The comparison, step by step

Your home's heat demand is the heat delivered into the rooms each year. Your boiler burns more fuel than that, because it is not 100% efficient, so your current cost is heat demand divided by boiler efficiency, times your fuel rate.

The heat pump delivers the same heat using electricity equal to heat demand divided by its SCOP. At a SCOP of 3.4, 12,000 kWh of heat needs about 3,530 kWh of electricity. Multiply by your electricity rate for the running cost.

The result is the difference. Against mains gas on a standard tariff, a heat pump often lands close to level; a heat-pump tariff usually tips it cheaper. Against oil, LPG or electric heating it is normally cheaper to run. We take the £7,500 grant off the typical £11,500 install.

An estimate, not a quote
Real performance depends on system design, your radiators or underfloor heating, and how you run it. Read are heat pumps worth it and the Boiler Upgrade Scheme guide. See our disclaimers.