Energy and running costs
Annual running cost: heat pump compared with a gas boiler
- where
- heat pump electricity use (kWh/yr)
- annual heat demand (kWh/yr)
- seasonal performance, SCOP or SPF
- heat pump running cost (£/yr)
- electricity unit rate (p/kWh)
- boiler gas use (kWh/yr)
- boiler seasonal efficiency (%)
- gas boiler running cost (£/yr)
- gas unit rate (p/kWh)
- annual saving with the heat pump (£/yr)
Explain this equation
Compares a year's fuel bill for a heat pump with a gas boiler meeting the same heat demand. Use it to give a customer an honest running cost comparison.
A heat pump delivers S units of heat for each unit of electricity, so its electricity use is the demand divided by S. A boiler wastes some gas, so its gas use is the demand divided by its efficiency as a fraction. Multiplying each by the unit rate in pence and dividing by 100 gives pounds. The saving is the difference.
Fuel in equals heat out divided by efficiency; cost equals fuel times price.
Sense check: 15,500 kWh at SCOP 3.1 is 5,000 kWh of electricity. At about 26p that is around £1,320; the boiler at 90% uses about 17,200 kWh of gas, around £1,370 at 8p.
Watch out: standing charges are left out, and removing the gas supply saves that too. The result swings a lot with SCOP and tariff, so try a few values.
Compares the yearly fuel cost of meeting the same heat demand with a heat pump and with a gas boiler, using unit rates only.
Enter your values to see the result.
Good to know
Default tariffs are the Ofgem price cap averages for 1 October – 31 December 2026 by direct debit (electricity 26.32 p/kWh, gas 7.97 p/kWh); put in the customer’s own rates, or a weighted average if they are on a heat pump time-of-use tariff. SCOP is the rated seasonal figure to BS EN 14825 at the design flow temperature; MCS 031 uses a seasonal performance factor (SPF) from its tables, e.g. 3.1 in its worked example. Standing charges are left out: add the gas standing charge (29.68 p/day in that period) to the saving if the gas supply will be capped off.
Common mistake
Using the SCOP for 35 °C flow when the system will actually run at 50–55 °C. Seasonal performance drops noticeably as flow temperature rises.
Limits
Unit-rate comparison only: no standing charges, maintenance or tariff changes. Accuracy depends on the demand figure and the real seasonal performance achieved.
Sources
- MCS 031 Issue 4.0 Heat pump pre-sale information and calculations (Pspecific = 1000 × Q / (24 × D); Pt = Pspecific × (21 − do); W/m²; Appendix A Table 1 degree days and outdoor low temperatures by postcode; Appendix B worked example)
- BS EN 14825 Air conditioners, liquid chilling packages and heat pumps: testing and rating at part load and calculation of seasonal performance (SCOP)
- Ofgem: Changes to energy price cap between 1 October and 31 December 2026 (direct debit averages: electricity 26.32 p/kWh, gas 7.97 p/kWh)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow MCS standards, manufacturer data, BS 7671, the ENA connection rules and Building Regulations. System design and DNO applications need a competent, certified installer.