Heat pump in a 1960s semi
Cavity walls that are usually fillable, but often large single-glazed-era window openings and minimal floor insulation. Better than Victorian, worse than modern.
With the radiators as they are
Saves £61
a year · existing radiators, average size
With upgraded radiators
Saves £218
a year · SCOP 3.4
What to do first
Cavity fill and loft insulation are cheap and effective here. With those done the heat pump numbers improve markedly.
Upgrading the radiators is worth about £157 a year in this house — which is the difference between a heat pump being a good idea and a questionable one.
The numbers behind that
- Typical gas use for this kind of house: about 14,000 kWh a year.
- That is roughly 11,900 kWh of actual heat, once boiler losses are taken off.
- A heat pump on the existing radiators would use about 4,103 kWh of electricity to deliver it.
- Break-even electricity price: 27.59p per kWh. The cap is currently 26.11p.
If your break-even price is above the price you actually pay, the heat pump wins. If it is below, it does not — and no amount of enthusiasm changes that arithmetic. A dedicated heat pump tariff can move your real price down enough to flip it.