Heat pump in a detached house
More external wall per square metre of floor means more heat loss. Bigger bills either way, which cuts both ways — the savings from getting it right are bigger too.
With the radiators as they are
Saves £51
a year · existing radiators, average size
With upgraded radiators
Saves £242
a year · SCOP 3.4
What to do first
Larger houses justify the radiator upgrade more easily, because the annual saving is bigger against the same one-off cost.
Upgrading the radiators is worth about £191 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 17,000 kWh a year.
- That is roughly 14,450 kWh of actual heat, once boiler losses are taken off.
- A heat pump on the existing radiators would use about 4,983 kWh of electricity to deliver it.
- Break-even electricity price: 27.14p 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.