HeatPumpSwitch › Methodology
Methodology: exactly how every figure on this site is produced
Nothing here is a quote and nothing here is a promise. This page states every assumption we use, so that any saving figure you see elsewhere on the site can be checked against it — which is what the CAP Code and the Green Claims Code require of anyone making a saving claim.
Energy prices we use
Ofgem energy price cap, 1 July – 30 September 2026 (direct debit, average). Oil/LPG/coal are editable estimates, not primary-sourced.
https://www.ofgem.gov.uk/news/changes-energy-price-cap-between-1-july-and-30-september-2026
| Key | Value | Primary-sourced |
|---|---|---|
| electricity_per_kwh | £0.2611 | ✓ |
| electricity_heatpump_tariff_per_kwh | £0.2611 | — |
| gas_per_kwh | £0.0733 | ✓ |
| oil_per_litre | £0.62 | — |
| lpg_per_litre | £0.78 | — |
| coal_per_kg | £0.55 | — |
Rows marked “—” are editable editorial estimates, not primary-sourced figures. Oil, LPG and solid-fuel prices are not published as a regulated cap anywhere, so they are maintained by hand and flagged as such.
Existing-system efficiencies
| gas condensing | 90 % |
| gas non condensing | 75 % |
| oil | 85 % |
| lpg | 85 % |
| electric direct | 100 % |
| coal | 60 % |
SCOP assumptions
Realistic in-use SCOP by emitter/flow-temperature scenario. Catalogue SCOP at 35C is typically 4.2-5.0; field studies land lower. Sources: field-trial literature; treat as editorial assumption and state it wherever a saving is shown.
| underfloor 35 | 3.9 |
| oversized radiators 45 | 3.4 |
| existing radiators 50 | 3.0 |
| existing radiators 55 | 2.8 |
| small radiators 60 | 2.5 |
| catalogue claim 35 | 4.2 |
The calculation, step by step
- Metered fuel × calorific value = fuel energy in kWh (gas m³ × 10.55 kWh/m³).
- Fuel energy × seasonal efficiency of the existing boiler = delivered heat. This is the only quantity that is comparable between systems.
- Delivered heat ÷ SCOP = heat pump electricity.
- Electricity × unit rate + standing charge = heat pump annual cost.
- Fuel energy × unit rate + standing charge = current annual cost.
- (Capital cost − grant) ÷ annual saving = simple payback, with no discount rate, no fuel-price inflation and no maintenance difference.
What this cannot tell you
- We do not know your tariff. If you are not on a standard variable tariff at the cap, every electricity figure here is wrong for you — usually in your favour on a heat pump tariff.
- We do not know your building. Two 1930s semis with the same floor area can differ by 40 % in heat demand depending on what has been done to the loft and the windows.
- We do not know how your system will be commissioned. A heat pump set to a 55 °C flow temperature when 45 °C would do loses roughly 15 % of its efficiency, and no calculator can predict that in advance.
- Simple payback ignores the cost of capital, future price movements, and the fact that a boiler would also have needed replacing at some point.
Compliance
Every saving figure on this site is shown next to the energy price, SCOP, house type and year it assumes. That is a requirement of the CAP Code and the Competition and Markets Authority's Green Claims Code, and it is also the only honest way to publish a number like this. We never claim a fixed pound saving without those conditions attached, and we are not MCS certified or accredited.