Most heat-pump running-cost disappointments come from weak assumptions, not from the technology itself. If you start with realistic demand, realistic SCOP, and your actual tariff, you get a planning range you can trust.
Use this page as a homeowner decision framework: start with a quick answer, run a clearly labelled example, and then compare conservative versus optimistic assumptions before you spend.
All figures in this article are broad estimates. Energy prices, fuel quality, installer design, weather, grants, and household habits can change the result, so use the numbers as a planning guide rather than a guarantee.
Quick answer
In plain terms: annual running cost is usually estimated as annual useful heat demand ÷ SCOP × electricity unit price.
If you are replacing gas, oil, or direct electric heat, compare on useful heat delivered and always test at least one cautious scenario.
Use your own bill history where possible. National averages are a fallback, not the best decision input.
Worked example (illustrative)
Example only: assume annual useful heat demand is 14,000 kWh, planned SCOP is 3.1, and electricity is 28p/kWh. Estimated heating electricity use is 14,000 ÷ 3.1 = 4,516 kWh.
Estimated annual heating cost is 4,516 × GBP0.28 = GBP1,264. If the same home used gas at 7p/kWh with an 88% boiler, the comparable gas fuel cost would be around GBP1,114. That gap can narrow or reverse if SCOP rises, electricity tariff improves, or boiler performance is worse than assumed.
Label this as a scenario, not a promise. Your installer design temperature, radiator output, and controls have a bigger impact than brochure numbers.
Cost drivers comparison table
Use this as a practical sense-check before requesting formal quotes.
| Input | Conservative case | Optimistic case |
|---|---|---|
| SCOP | 2.8 | 3.6 |
| Electricity unit price | 32p/kWh | 24p/kWh |
| Annual heat demand | 16,000 kWh | 12,000 kWh |
| Estimated annual cost | About GBP1,829 | About GBP800 |
Decision tree: should you trust your first estimate?
If you used real annual bills and a room-by-room heat-loss survey, continue to quote comparison.
If you used floor-area assumptions only, run the calculator again with a low/medium/high demand range.
If you are unsure about SCOP, compare at least three values (for example 2.8, 3.2, 3.6) and keep only decisions that still make sense in the cautious case.
Quick checklist before acting on the number
Check whether your electricity tariff is flat-rate or time-of-use.
Check whether hot-water production is included in your annual demand assumption.
Check whether standing charges are materially different between options.
Check whether your quote includes emitter upgrades and commissioning.
Official-source summary (UK and Ireland)
For UK readers, Ofgem and UK government energy publications are useful for market context and tariff trends.
For Ireland, the Commission for Regulation of Utilities and SEAI publications are useful for local price context and retrofit guidance.
Always match official market data to your own bill history before making a final spending decision.
Common mistakes to avoid
- Using a single SCOP figure without testing a cautious range.
- Comparing fuel prices without converting to useful heat output.
- Ignoring methodology assumptions when sharing calculator results.
Conclusion
A robust running-cost estimate is a range, not one number. Keep a cautious scenario in every decision.
Use the calculator, then verify assumptions against the methodology page and your own annual bills.