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Heat pump vs gas boiler: a 2012 onwards detached house
A worked example with this building's own numbers, not an average. Everything below is calculated from the assumptions listed with it, and you can change any of them in the calculator.
Assumptions behind these figures
- House: detached house, 2012 onwards, 140 m²
- Space-heat demand as found 50 kWh/m²/yr
- SCOP 3.9 @ 35 °C
- Assumed existing boiler efficiency 92 %
- Ofgem energy price cap, 1 July – 30 September 2026 (direct debit, average). Oil/LPG/coal are editable estimates, not primary-sourced.
- Capital cost £13,000
- Simple payback: no discount rate, no fuel-price inflation, no maintenance difference. Figures are calculations, not quotes.
Fabric and demand
| Treated floor area | 140 m² |
| Space-heat demand as found | 50 kWh/m²/yr |
| Annual space heating | 8,400 kWh |
| Hot water | 2,200 kWh |
| Total delivered heat | 10,600 kWh |
| Implied heat loss | 4.7 kW |
| Assumed design flow temperature | 35 °C |
| Assumed SCOP | 3.9 |
| Assumed existing boiler efficiency | 92 % |
How these numbers were produced
- Delivered heat needed: 8,400 kWh (space) + 2,200 kWh (hot water) = 10,600 kWh
- Fuel energy at 92 % seasonal efficiency: 10,600 ÷ 0.92 = 11,522 kWh
- Current annual cost: 11,522 kWh × £0.0733 + £315 standing charges = £1,159
- Heat pump electricity: 10,600 kWh ÷ SCOP 3.9 = 2,718 kWh
- Heat pump annual cost: 2,718 kWh × £0.2611 + £209 standing charge = £918
- Running-cost difference: £1,159 − £918 = £241
Investment and payback
| Installed cost, typical air source | £13,000 |
| Grant | −£7,500 |
| Net capital cost | £5,500 |
| Annual running-cost saving | £241 |
| Simple payback | 22.8 years |
Boiler Upgrade Scheme, £7,500 (air source)
What actually decides it in this house
35 °C and a SCOP near 3.9 puts this house ahead of a gas boiler on running cost alone, before any grant. The question here is only capital cost and payback.
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