How this comparison works
“Heat pump or gas boiler?” has two halves that pull in opposite directions. Per kWh of heat, a heat pump is much cheaper to run unless electricity is very expensive, but it costs considerably more to install. So a fair comparison has to cover the whole ownership period, not just the annual bill. This calculator sets both systems side by side over 15 years (adjustable) and accounts for:
- energy: heat demand ÷ SCOP for the heat pump, heat demand ÷ seasonal efficiency for the boiler;
- separate price paths for electricity and gas (in the EU gas is likely to rise faster once ETS2, carbon pricing for buildings, starts);
- upfront cost net of grants;
- maintenance, growing 2% a year;
- the gas standing charge, which you stop paying only if you leave the gas network;
- replacement of equipment that wears out inside the comparison period;
- CO₂ from both systems.
You get the cumulative cost curves, the year the heat pump overtakes the boiler, the discounted total cost of ownership (NPV) and the electricity/gas price ratio at which annual running costs are equal.
The formula
Worked example
The defaults assume 12,000 kWh of heat a year, a SCOP of 3.2, a 90% condensing boiler, electricity at 0.28 €/kWh and gas at 0.10 €/kWh. The heat pump uses 3,750 kWh of electricity (1,050 €); the boiler burns 13,333 kWh of gas (1,333 €).
Add servicing (150 € for the heat pump, 120 € for the boiler) and the 110 € gas standing charge that goes away when you disconnect, and year-one running costs come to ≈ 1,200 € for the heat pump and ≈ 1,563 € for the boiler. That’s a saving of about 363 € a year.
Upfront, the heat pump costs 13,000 € minus a 3,000 € grant, so 10,000 €, against 3,500 € for a new boiler: 6,500 € more. With electricity rising 2% and gas 3% a year, the heat pump’s cumulative cost drops below the boiler’s after about 12.7 years. After 15 years it is ahead by roughly 1,670 € in nominal terms. Discounted at 4%, the two are almost level (25,160 € vs 24,490 €), a sign of how much the result depends on the grant and on prices.
Your price ratio is 0.28 ÷ 0.10 = 2.8, and the break-even ratio is 3.77 (3.56 on energy alone; saving the gas standing charge lifts it). CO₂ falls from 2.44 t to 1.31 t a year on a 350 g/kWh grid, about 17 t over 15 years.
How to read the results
- 15-year cost difference (headline): a positive figure means the heat pump is cheaper over the period, all costs included.
- Break-even year is when running savings have repaid the extra upfront cost. Compare it with the heat pump’s 15–20-year life.
- Break-even price ratio vs your ratio: the further your ratio sits below break-even, the better the investment holds up if prices change.
- NPV of TCO discounts future costs, which favours the option with the lower upfront cost. Use your mortgage or savings rate.
- Annual running cost vs electricity price chart: the crossing point is the electricity price above which gas becomes cheaper to run.
Typical values
| Country (2024–25, approx.) | Electricity / gas price ratio | Break-even ratio at SCOP 3.2 | Typical verdict |
|---|---|---|---|
| United Kingdom | 3.5–4.0 | 3.6 | Marginal on running cost; grant decides |
| Germany | 2.5–3.0 | 3.6 | Heat pump cheaper to run |
| France | 2.0–2.5 | 3.6 | Heat pump clearly cheaper |
| Netherlands | 2.0–2.5 | 3.6 | Heat pump clearly cheaper |
| Sweden / Norway | 1.5–2.5 | 3.6 | Heat pump dominant |
| United States (average) | 3.0–3.5 | 3.6 | Depends strongly on state |
Ratios move with tariffs, so check your own bills. Heat-pump tariffs or time-of-use rates can lower the effective ratio by 20–40%.
Tips
- Compare at replacement time. When the boiler fails, the real choice is heat pump versus a new boiler, and that’s what this calculator models by default.
- Push the SCOP up. Larger radiators and weather compensation can lift SCOP from 2.7 to 3.5, which is worth more than most tariff tweaks. Estimate your SCOP with the heat pump calculator.
- Disconnect from gas if you cook on electricity. The standing charge alone is often 100–150 a year.
- Reduce demand first. Every kWh of heat you avoid with insulation lowers the running cost and the size of heat pump you need.
- Look at all fuels. Off the gas grid? Compare oil, LPG and pellets in the heating cost comparison.
Limitations
The comparison assumes a constant SCOP and boiler efficiency over the period; badly commissioned heat pumps or oversized boilers can fall short. Grid carbon intensity is held constant, so the CO₂ savings are conservative. Financing costs, effects on property value, cooling (reversible heat pumps) and possible future gas-network levies are left out. Installation costs vary widely by country and house, so get at least two quotes and enter them.
Method & assumptions
Heat-pump electricity = heat demand ÷ SCOP; boiler gas = heat demand ÷ seasonal efficiency. Year-1 running cost adds maintenance and (for gas, or for the heat pump if you stay connected) the standing charge. Costs are projected with separate electricity and gas escalation rates, maintenance +2%/yr and like-for-like replacement at end of life.
Break-even price ratio: the electricity ÷ gas price at which annual running costs are equal, r* = [Q/η·pgas − ΔF] / (Q/SCOP) / pgas, where ΔF is the heat pump's extra fixed cost (maintenance minus any standing charge saved). Without fixed costs this collapses to r* = SCOP ÷ η.
Frequently asked questions
Is a heat pump cheaper than a gas boiler?
What electricity-to-gas price ratio makes a heat pump worthwhile?
How long does a heat pump last compared with a gas boiler?
Are heat pumps more expensive to maintain?
How much CO₂ does a heat pump save compared with gas?
Should I replace a working gas boiler with a heat pump?
Sources & references
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