The Numbers That Matter
To compare running costs fairly, you need three figures: the efficiency of each system, the fuel price, and your home’s annual heat demand.
Gas boiler: A modern condensing boiler operates at roughly 90% efficiency in real-world conditions (not the 94% on the data sheet). At a gas price of 7p/kWh, the cost per kWh of useful heat is about 7.8p.
Air source heat pump: A well-designed system achieves a seasonal COP (SCOP) of 3.5–4.0. At an electricity price of 24p/kWh, the cost per kWh of useful heat is 6–6.9p.
For a typical three-bedroom house with an annual heat demand of 12,000 kWh, that translates to:
- Gas boiler: £936/year
- Heat pump: £720–£828/year
The heat pump is already cheaper to run — and this gap widens significantly with solar panels.
Add Solar and the Gap Widens
If you pair your heat pump with a 4 kWp solar array, you can generate 3,400–3,800 kWh of free electricity per year. Much of this can be used directly by the heat pump, especially with smart scheduling.
Realistically, solar might cover 30–40% of your heat pump’s annual electricity consumption, saving an additional £200–£300 per year. Your effective heating cost drops to around £450–£550/year — roughly half the cost of gas.
The Price Cap Factor
Gas prices are subject to the Ofgem price cap and international wholesale markets. Over the past five years, gas prices have fluctuated wildly — from 3p/kWh in 2020 to over 10p/kWh in 2022–2023.
Electricity prices are also volatile, but there is a crucial difference: with solar panels and battery storage, you can generate your own electricity. You cannot generate your own gas. This energy independence is a significant long-term advantage.
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Maintenance Costs
A gas boiler requires an annual service (£80–£120) and has an average lifespan of 12–15 years. A heat pump also needs an annual service (similar cost) but typically lasts 20–25 years.
Over 20 years, you are likely to need at least one boiler replacement (£2,500–£4,000), while your heat pump should still be running. Factor this in and the lifetime cost difference becomes very significant.
Worked Example: A Full Year of Bills Compared
Let us run the numbers for a real three-bedroom Leicester semi with an annual heat demand of 12,000 kWh, using 2026 prices (electricity ~24p/kWh, gas ~7p/kWh).
- Gas boiler (90% efficient): 12,000 ÷ 0.90 = 13,333 kWh of gas × 7p = £933 a year, plus the standing charge for keeping the gas connection.
- Heat pump (SCOP 3.6): 12,000 ÷ 3.6 = 3,333 kWh of electricity × 24p = £800 a year — and you can drop the gas standing charge entirely if this is your last gas appliance.
- Heat pump on a smart heat-pump tariff: shifting the bulk of heating into cheaper off-peak windows can pull the effective rate down and take the annual figure toward £600–£700.
- Heat pump + 4kWp solar: free daytime generation covering 30–50% of the electricity can bring the net heating cost down to roughly £450–£550 a year.
The headline: even before solar or a specialist tariff, a well-designed heat pump already beats gas on running cost — and unlike gas, every lever (solar, battery, time-of-use tariff) is yours to pull. The one thing that undoes all of this is a badly designed system running at 55–60°C flow temperatures, which is exactly why we design for 35–45°C.
Frequently asked questions
Yes, when designed well. At a COP of 3.5–4.0 a heat pump delivers heat at roughly 6–7p per kWh versus about 7.8p from a 90%-efficient gas boiler. For a typical 12,000 kWh home that is around £720–£828 a year versus £936 on gas — and the gap widens with solar.
Per unit, gas is cheaper (about 7p/kWh vs 24p/kWh for electricity). But a heat pump uses roughly a quarter of the units a boiler burns because it moves heat rather than making it, so the cost per unit of useful heat ends up lower than gas.
Heat-pump-specific and time-of-use tariffs (such as Octopus Cosy or similar smart tariffs) offer cheaper off-peak windows. Combined with a well-designed system you can shift usage to the cheapest hours and cut annual costs further — see our best heat pump tariff guide.
A 4kWp array generates 3,400–3,800 kWh a year and can realistically cover 30–50% of a heat pump's electricity, saving £200–£300+ annually and pushing effective heating costs towards £450–£550 a year.
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