Heat pump vs gas boiler running costs: questions to ask
Running costs depend more on sizing, flow temperature and your tariff than on the brand of heat pump you buy – here's what to check before you sign.
The short answer
A well-sized air source heat pump almost always costs less to run than the gas boiler it replaces once you factor in the Boiler Upgrade Scheme grant and 0% VAT on the installation, but "almost always" hides a lot of variation. Installing one typically costs £10,100 – £16,800 before any grant, against £2,200 – £3,650 for a new gas boiler – so the real question homeowners should be asking isn't "what does it cost to fit", it's "how efficiently will this one run in my house." That depends far more on the installer's design decisions than on the make of heat pump on the wall.
Why running costs vary so much between two "identical" installs
A heat pump doesn't burn fuel to make heat – it moves heat from the outside air into your home, and for every unit of electricity it uses it typically delivers several units of heat. That multiplier (the Seasonal Coefficient of Performance, or SCOP) is the single biggest factor in your running costs, and it isn't fixed: it depends on how hot the water needs to be to heat your radiators, how well the system is controlled, and how accurately it was sized to your home's heat loss.
Electricity costs more per unit than gas, so a heat pump only wins on running costs if it's efficient enough to make up that gap. Run one at a low "flow temperature" (the water temperature leaving the unit into your pipes) with radiators or underfloor heating sized to suit, and it will usually beat a gas boiler comfortably. Run the same unit hard, at boiler-like flow temperatures, through radiators that are too small for the job, and the running-cost advantage shrinks or disappears.
Questions worth asking before you sign
- What design flow temperature are you installing to, and why? Lower is generally better for running costs; ask what it will be on the coldest day of the year, not just an average day.
- Have you done a room-by-room heat loss survey, or sized the unit on a rule of thumb? Oversizing wastes money upfront and on standing losses; undersizing means the backup immersion heater kicks in more often, which is expensive.
- Will any radiators need to be upsized? This is one of the most common hidden costs in a heat pump quote – ask for it in writing before you commit.
- What controls come with it, and can you see real-time efficiency data? Weather compensation (adjusting flow temperature to outdoor conditions automatically) generally helps running costs more than a smart thermostat alone.
- Is the installer MCS certified? You need this for the Boiler Upgrade Scheme grant, and it's also a reasonable proxy for design competence.
- How was the hot water cylinder sized and insulated? A heat pump heating a poorly lagged cylinder on a long cycle will cost more to run than the headline efficiency figures suggest.
If you're comparing more than one quote, our "is my quote fair" tool is worth running each one through before you decide – it flags prices and specifications that look out of line with similar jobs.
The install-cost side of the comparison
It's still worth knowing where the two technologies sit on installation price, because the grant materially changes the comparison. In England, Wales and Scotland the Boiler Upgrade Scheme or Home Energy Scotland grant takes up to £7,500 off an MCS-certified heat pump install, and installing one currently qualifies for 0% VAT (until 31 March 2027), while a straight like-for-like boiler swap is charged at the standard rate. See our Air source heat pump guide for a full breakdown by size and property type.
If you're simply replacing a failed boiler rather than weighing up a switch, it's also worth checking what a gas boiler itself would cost today – the type you choose changes the price more than most people expect:
| Material | Typical | Usual range | Lifespan |
|---|---|---|---|
| Combi boiler (like-for-like) | £2,800 | £2,200 – £3,650 | 12-15 years |
| Regular (heat-only) boiler, tanks kept | £2,800 | £2,200 – £3,650 | 12-15 years |
| System boiler (existing cylinder kept) | £3,050 | £2,400 – £4,000 | 12-15 years |
| Convert regular or system to combi | £3,800 | £2,950 – £4,950 | 12-15 years |
Our New boiler guide covers which of those is likely to suit your system.
Cutting running costs further, after the heat pump is in
A few things move the needle once the unit is installed and running:
- Insulation first. A heat pump heating a leaky house works harder and less efficiently than the same unit in a well-insulated one – loft and wall insulation pay back faster when paired with a heat pump than with a gas boiler.
- Solar panels and a battery, if you have roof space, reduce the electricity bill a heat pump adds, particularly if you can run it more during daylight hours. Our Solar panels guide has current costs by system size.
- Your electricity tariff matters. Some suppliers offer tariffs with cheaper off-peak rates aimed at heat pump and EV owners; whether one is worth switching to depends on your usage pattern, not a fixed answer.
The bottom line
Don't judge a heat pump quote on install price alone, and don't take a stated running-cost saving on faith either – ask how the system has been designed to hit it. The grant and 0% VAT narrow the upfront gap with a gas boiler considerably; a careful sizing and flow-temperature design is what decides whether that advantage shows up on your electricity bill too.