Whether a heat pump is cheaper to run than a gas boiler depends on two things: how efficient each system is, and the price you pay per unit of electricity and gas. You can compare them yourself with one simple calculation.
The key idea: cost per unit of heat
Cost per kWh of heat = price per kWh of energy ÷ efficiency
A modern condensing gas boiler is typically around 85% to 92% efficient. A heat pump’s efficiency is described by its seasonal coefficient of performance (SCOP), commonly in the range of about 2.5 to 4, meaning it delivers several units of heat for each unit of electricity.
A worked example (illustration only)
These prices are hypothetical. Check the current Ofgem price cap and your own tariff for real figures. Suppose electricity costs 27p per kWh and gas costs 7p per kWh.
- Gas boiler at 90% efficiency: 7 ÷ 0.90 = about 7.8p per kWh of heat
- Heat pump with SCOP 3.2: 27 ÷ 3.2 = about 8.4p per kWh of heat
- Heat pump with SCOP 3.8: 27 ÷ 3.8 = about 7.1p per kWh of heat
In this example the two are close, and a well-designed heat pump can come out slightly ahead. If the electricity-to-gas price ratio rises, the heat pump loses ground. If it falls, or you use a time-of-use tariff, it gains.
What changes the heat pump’s efficiency
- Insulation and heat loss. A well-insulated home needs less heat, so the system runs more gently.
- Flow temperature. Larger radiators or underfloor heating let the system run at a lower temperature, which improves efficiency.
- System design. Correct sizing, a suitable hot water cylinder and good controls matter more than the brand.
Other costs to compare
- Installation cost after the up-to-£7,500 Boiler Upgrade Scheme grant, where it applies to you.
- Standing charges. Removing your gas connection can save the gas standing charge.
- Servicing and expected equipment life.
- Radiator, pipework and cylinder changes, which can add to the quote.
How to do it for your home
- Find your current gas and electricity unit prices on your bill.
- Ask each installer for the predicted SCOP and annual running cost for your house.
- Compare totals over 10 to 15 years, including installation costs and the grant.
Our UK calculator can help you put these numbers together.
Beyond running costs
Running costs are only one part of the decision. A gas boiler is cheaper to buy and simple to replace, but it ties you to a fuel that is being phased out of new homes and has uncertain long-term prices. A heat pump costs more up front, but the grant narrows the gap, and it can supply cooling in some models. Over 15 years, installation cost, servicing and the price ratio between electricity and gas decide which is cheaper in your case.
A quick checklist before you decide
- Is your home reasonably insulated, with loft insulation and no major draughts?
- Do you have space outside for the unit and inside for a hot water cylinder?
- Are your radiators large enough, or can key ones be upgraded?
- Can you take advantage of a smart or time-of-use electricity tariff?
- Does the installer’s design show the expected SCOP for your home?
Common myths
“Heat pumps don’t work in the cold.” Modern air-source heat pumps work in UK winters, though efficiency falls as it gets colder. “You need underfloor heating.” Not necessarily. Many homes use radiators, sometimes with a few larger ones. “They always cost more to run.” It depends on the price ratio and on the system design, as the example above shows.
More questions
Can I keep my gas boiler as backup? It is possible, but BUS requires replacing the fossil fuel system, so ask your installer how that affects the grant.