HeatPumpSwitch › By house type › a 1945-1966 semi-detached house
Heat pump vs gas boiler: a 1945-1966 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, 1945-1966, 95 m²
- Space-heat demand as found 150 kWh/m²/yr
- SCOP 3.0 @ 50 °C
- Assumed existing boiler efficiency 80 %
- 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 | 150 kWh/m²/yr |
| Annual space heating | 14,250 kWh |
| Hot water | 1,800 kWh |
| Total delivered heat | 16,050 kWh |
| Implied heat loss | 7.9 kW |
| Assumed design flow temperature | 50 °C |
| Assumed SCOP | 3.0 |
| Assumed existing boiler efficiency | 80 % |
How these numbers were produced
- Delivered heat needed: 14,250 kWh (space) + 1,800 kWh (hot water) = 16,050 kWh
- Fuel energy at 80 % seasonal efficiency: 16,050 ÷ 0.80 = 20,062 kWh
- Current annual cost: 20,062 kWh × £0.0733 + £315 standing charges = £1,785
- Heat pump electricity: 16,050 kWh ÷ SCOP 3.0 = 5,350 kWh
- Heat pump annual cost: 5,350 kWh × £0.2611 + £209 standing charge = £1,606
- Running-cost difference: £1,785 − £1,606 = £180
Investment and payback
| Installed cost, typical air source | £13,000 |
| Grant | −£7,500 |
| Net capital cost | £5,500 |
| Annual running-cost saving | £180 |
| Simple payback | 30.6 years |
Boiler Upgrade Scheme, £7,500 (air source)
What actually decides it in this house
At 50 °C the SCOP is about 3.0, still under the 3.6 gas break-even. The gap is small enough that a heat pump tariff, or upsizing the three or four worst radiators, flips the answer. Get the room-by-room calculation before you decide.
Advertising
Get quotes for your property
Compare at least three installers. Ask each one for the heat-loss calculation and the design flow temperature in writing — that number decides your running cost more than the brand on the box.
Ad. If you request a quote through this link we may be paid a commission by the installer. It does not change your price, and we do not rank companies by how much they pay.