Answer first
Start with the heat delivered to the rooms and hot water—not the headline price of a litre or an electricity unit. Oil bought at 6.7p/kWh and burned at 80% efficiency costs about 8.4p per useful kWh. Electricity at 24.7p/kWh through a heat pump achieving an SPF of 3 costs about 8.2p per useful kWh.
That worked example is almost level. A better-performing heat pump, a suitable smart tariff or expensive oil moves the result towards the heat pump; low oil prices, high electricity prices or poor system performance move it the other way. Use your invoices and a surveyed design rather than a national promise.
Energy Saving Trust average oil-price assumption when last reviewed
View sourceEnergy Saving Trust standard-rate electricity assumption when last reviewed
View sourceMedian whole-system SPFH4 in the Catapult monitored sample
View sourceGet an oil-to-heat-pump cost comparison for your home
Share the property, postcode, current heating and the cost question you want answered. FLO will explain what can be estimated now and what needs a survey before a figure is reliable.
Convert both fuels into useful heat
An oil invoice records fuel delivered, not heat that reached the home. Convert the fuel to kilowatt-hours, then multiply by a defensible seasonal boiler efficiency. For a household using 1,500 litres, a rough 10.2kWh per litre gives 15,300kWh of fuel input; at 80% seasonal efficiency that is about 12,240kWh of useful heat.
A heat pump supplying the same 12,240kWh would use about 4,371kWh of electricity at SPF 2.8, 4,080kWh at SPF 3 and 3,497kWh at SPF 3.5. Add any separately metered immersion or backup-heater use and use the household tariff to price the result.
Keep in mind: Oil energy content and boiler efficiency vary. Use deliveries over several representative years and have the installer sense-check the result against the room-by-room heat loss.
Compare current prices without pretending they stay fixed
Energy Saving Trust currently publishes smoothed assumptions rather than a forecast: 6.7p/kWh for oil and 24.7p/kWh for standard electricity. At those rates, the break-even SPF against an 80%-efficient oil boiler is about 2.95. Against a 70%-efficient boiler it is about 2.58.
Oil can move sharply between deliveries and electricity rates change by tariff and period. A useful decision sheet therefore shows at least three scenarios—for example low, central and high oil prices—plus two heat-pump performance cases. That is more honest than quoting one annual saving to the nearest pound.
Include the costs that disappear or remain
Replacing oil may remove fuel deliveries, tank inspections and oil-boiler servicing. It may also create a one-off tank decommissioning cost. A heat pump still needs planned maintenance, and its electricity bill may include hot water, circulation pumps and occasional direct electric backup.
If solar, battery storage or a time-of-use tariff is part of the plan, model it separately. Solar production is seasonal and cannot simply be subtracted from winter heating demand. The comparison should show the base heat-pump case before optional technology is credited.
- Three years of oil deliveries where available
- Current electricity tariff and meter arrangement
- Rooms or floor area heated now versus after the change
- Hot-water habits and any immersion use
- Proposed seasonal efficiency and design flow temperature
Ask for a range tied to the survey
The room heat loss, radiator schedule and flow temperature determine whether the proposed SPF is plausible. An installer should show the assumptions and explain what would make the estimate better or worse.
FLO can compare the existing oil use with the surveyed heat demand and put the calculation beside the written quote. The output is still an estimate, but it is one a homeowner can audit and update when prices change.
What to read next
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Questions people also ask
Will every oil-heated home save money with a heat pump?+
No. Savings depend on oil price, electricity tariff, present boiler efficiency, heat demand and the installed heat pump’s seasonal performance.
How many kWh are in a litre of heating oil?+
A rough conversion is around 10.2kWh of fuel input per litre. The useful heat is lower because no boiler is 100% efficient.
Should I use one oil delivery to estimate annual demand?+
Prefer several full years and note changes in occupancy, weather, hot-water use or rooms heated. A single delivery may not cover a complete season.
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: how energy-saving figures are calculatedCurrent household fuel-price assumptions, carbon factors and the method used to keep savings estimates current.
- UK Government: calorific values and density of fuelsOfficial energy-statistics reference data used when converting delivered heating fuel into energy.
- 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.