Answer first
Compare the cost of delivering the same amount of useful heat. A gas boiler buying cheaper energy can still lose much of that advantage because it delivers less than one unit of heat per unit of fuel, while a well-designed heat pump can deliver several.
The result changes with flow temperature, radiator sizing, controls, tariff and whether removing gas also removes its standing charge. A credible quote should show every assumption instead of promising a universal percentage saving.
Heat pumps can deliver more than three units of heat for each unit of electricity under suitable conditions
View sourceMedian whole-system SPFH4 in a monitored 291-system sample
View sourceThe fair comparison is equal useful heat and room temperatures
View sourceCompare a heat pump with gas for your home
Share the property, current heating and the question holding up your decision. FLO will explain what to check next without pushing you into a survey.
Compare heat delivered, not just unit prices
Gas and electricity prices are quoted per kilowatt-hour bought. The home pays for useful heat after system losses and efficiency are considered. Divide the gas price by realistic boiler efficiency and the electricity price by a defensible heat-pump seasonal performance figure.
Then compare like with like. If the heat pump heats more rooms for longer, the household may buy more useful heat even though the system itself is efficient.
Design decides much of the heat-pump side
Lower water temperatures generally support better efficiency. The survey should therefore connect room heat loss, radiator output, pipe flow and the proposed weather-compensation curve.
An oversized or poorly commissioned system can cycle; undersized emitters may force hotter water. Either problem can weaken the saving assumed in a headline calculator.
Tariffs and standing charges can move the answer
Use the electricity and gas rates on your own bills. Smart or heat-pump tariffs may help when the home can shift hot-water production or modest preheating, but the whole meter must be compared.
If gas is removed completely, include the avoided gas standing charge. If the cooker or another appliance keeps the gas account open, that saving does not exist.
Ask for a range, not a promise
A useful proposal shows annual heat demand, assumed seasonal efficiency, tariff rates and the estimated electricity range. It should explain what would move the result up or down.
FLO treats that calculation as a decision aid. The room-by-room survey and emitter design are what make the assumptions property-specific.
What to read next
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Questions people also ask
Are heat pumps always cheaper than gas?+
No. Design, tariffs, comfort and the home’s heat demand determine the result.
Should I include my gas standing charge?+
Only if the installation lets you close the gas account completely.
Is a high catalogue COP enough?+
No. Use seasonal whole-system performance at relevant temperatures, not one test point.
Evidence used for this answer
Figures are explained in context and links go to the independent source. Prices, tariffs, scheme rules and standards can change, so check the source again before making a financial or technical decision.
- Energy Saving Trust: air source heat pumpsIndependent guidance on installation costs, running costs, suitability, radiators and household savings.
- Energy Systems Catapult: heat-pump performance analysisMeasured seasonal performance and cold-weather operation from the Electrification of Heat demonstration project.
- MCS heat-pump design standardTechnical requirements for heat loss, equipment selection, domestic hot water and system design.
- Ofgem: energy price cap unit ratesPublished electricity and gas unit-rate benchmarks. Rates vary by region, payment method, tariff and price-cap period.