Heat pumps are central to decarbonising heating in Europe and the US. Whether one saves you money comes down to a single comparison: efficiency vs price ratio.
Step 1: Your heat demand
How much heat does your home need in a year, in kWh? If you heat with gas now:
heat demand ≈ annual gas kWh × boiler efficiency
A modern condensing boiler might be around 85–90% efficient in practice. So 12,000 kWh of gas × 0.88 ≈ 10,560 kWh of heat.
Step 2: Electricity a heat pump needs
electricity kWh = heat demand ÷ SCOP
With a SCOP of 3: 10,560 ÷ 3 ≈ 3,520 kWh of electricity.
SCOP (seasonal COP) matters more than headline COP. Real-world SCOP depends on:
- Flow temperature: lower is more efficient. Bigger radiators or underfloor heating help.
- Climate: colder winters lower efficiency.
- Installation quality: sizing, controls, and commissioning.
Step 3: Compare costs
Illustrative prices (use your own):
| Gas boiler | Heat pump | |
|---|---|---|
| Energy bought | 12,000 kWh gas | 3,520 kWh electricity |
| Price | 7p/kWh | 25p/kWh |
| Annual cost | £840 | £880 |
At these prices it's roughly break-even. Change the inputs:
- SCOP 3.5 → 3,017 kWh × 25p = £754 (cheaper)
- Time-of-use tariff at 15p for most heating → much cheaper
The break-even rule
A heat pump is cheaper to run when:
SCOP > (electricity price ÷ gas price) × boiler efficiency
With 25p electricity, 7p gas, 0.88 efficiency: 3.57 × 0.88 ≈ 3.14. A SCOP above ~3.1 wins.
Ways to lower running costs
- Lower flow temperatures (often needs larger emitters)
- Heat-pump-specific tariffs or time-of-use tariffs
- Insulation first: less heat demand means a smaller, cheaper system
- Remove the gas standing charge if you disconnect gas entirely, which is a real saving
For appliance-level energy costs, my Electricity Cost calculator helps. For the UK cap and standing charges, see UK Energy Price Cap 2027.