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Heat pump vs gas boiler: a 2012 onwards semi-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: semi-detached house, 2012 onwards, 95 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 | 95 m² |
| Space-heat demand as found | 50 kWh/m²/yr |
| Annual space heating | 4,750 kWh |
| Hot water | 1,800 kWh |
| Total delivered heat | 6,550 kWh |
| Implied heat loss | 2.6 kW |
| Assumed design flow temperature | 35 °C |
| Assumed SCOP | 3.9 |
| Assumed existing boiler efficiency | 92 % |
How these numbers were produced
- Delivered heat needed: 4,750 kWh (space) + 1,800 kWh (hot water) = 6,550 kWh
- Fuel energy at 92 % seasonal efficiency: 6,550 ÷ 0.92 = 7,120 kWh
- Current annual cost: 7,120 kWh × £0.0733 + £315 standing charges = £837
- Heat pump electricity: 6,550 kWh ÷ SCOP 3.9 = 1,679 kWh
- Heat pump annual cost: 1,679 kWh × £0.2611 + £209 standing charge = £647
- Running-cost difference: £837 − £647 = £189
Investment and payback
| Installed cost, typical air source | £13,000 |
| Grant | −£7,500 |
| Net capital cost | £5,500 |
| Annual running-cost saving | £189 |
| Simple payback | 29.0 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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