Answer first
Calculate net upfront cost after confirmed funding, annual energy for equal useful heat, standing charges that genuinely change, service and expected replacement items. Run several fuel-price and heat-pump-performance scenarios instead of declaring one guaranteed winner.
For 12,000kWh of useful annual heat, gas at 6.5p/kWh through an 85%-efficient boiler costs about £918 before standing charge. Electricity at 24.7p/kWh through an SPF 3 heat pump costs about £988. At SPF 3.5 it is about £847. These are transparent examples using current EST price assumptions, not a 15-year price forecast.
A useful comparison period—but not a warranty or guaranteed life
View sourceEnergy Saving Trust current smoothed gas-price assumption
View sourceEnergy Saving Trust current smoothed standard electricity assumption
View sourceGet the inputs for a property-specific 15-year comparison
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.
Begin with net capital cost
List the complete heat-pump scope, confirmed grant and optional finance separately. Compare it with the complete boiler alternative, including flue, controls, cylinder or system work and any gas-supply changes.
Do not compare a funded whole-system heat-pump quote with the retail price of a boiler alone. Both sides need labour, VAT, enabling work and disposal.
Model equal useful heat
Use one annual space-and-water heat requirement. Divide it by the seasonal efficiency of each option, then multiply by the relevant fuel price. Add standing charges only where the choice creates or removes them.
Show at least a lower and higher heat-pump SPF and several price ratios. This reveals the conditions under which the decision changes and prevents a false single-point answer.
Add maintenance and replacement honestly
Include expected servicing based on each manufacturer and warranty. Allow for known consumables or protection plans without inventing a precise failure schedule.
A 15-year model may cross a major component or appliance replacement, but timing is uncertain. Put replacement in a sensitivity column rather than quietly assuming one technology lasts forever.
Treat non-cash differences separately
Comfort, hot-water behaviour, indoor and outdoor space, noise, emissions and future policy may matter even where the central cost cases are close. Keep these visible rather than converting every preference into a questionable pound value.
A survey can provide the heat demand, emitter work and expected performance needed to make the model property-specific. The spreadsheet should then be easy to update when tariffs change.
What to read next
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Questions people also ask
Can anyone know energy prices for the next 15 years?+
No. Use scenarios and update them; do not present one forecast as certain.
Should the gas standing charge be counted?+
Only count the amount that changes. If gas is disconnected entirely, its standing charge may disappear; if gas remains for cooking, it does not.
Does grant funding belong in the comparison?+
Yes, once eligibility and the offer are confirmed; show gross cost, grant and net cost separately.
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.
- Home Energy Scotland: heat pumpsCurrent Scottish guidance on typical costs, savings, lifespan, comfort and combining a heat pump with solar panels.
- 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.