For most UK homes the decision between a heat pump and a new gas boiler is not really about the boxes; it is about the house they will run. A gas combi is cheap to fit, familiar to every plumber and quietly obsolescent as the electricity grid decarbonises. A modern air source heat pump costs more up front, needs a properly designed emitter circuit, but runs on electricity that is already less carbon-intensive than gas and will continue to fall each year. The right answer depends on your fabric, your radiators, your grant eligibility and how long you plan to stay.
Install cost, after grants
A new gas combi lands at £2,200–£3,500 fitted for a straightforward replacement, £3,500–£5,000 if you are moving position or upsizing pipework. An air source heat pump for a typical three-bed semi is £11,000–£15,000 before grant; the £7,500 Boiler Upgrade Scheme grant brings that to £3,500–£7,500 fitted by an MCS-registered installer. On a cash basis the gap is smaller than the sticker prices suggest.
Running cost at 2026 UK prices
A gas combi in a well-insulated three-bed uses roughly 10,000 kWh of gas per year; at the current price cap that is around £630. A well-designed heat pump running at a seasonal COP of 3.5 delivers the same heat from about 2,850 kWh of electricity; at the cap that is around £780 on a standard tariff, but £430–£520 on a genuine heat-pump time-of-use tariff such as Cosy Octopus or Ovo Heat Pump Plus. On the right tariff the heat pump is cheaper to run; on a flat tariff the gas boiler still wins narrowly.
Comfort in the house
Gas boilers heat quickly and cycle on and off; the house is warm in bursts. Heat pumps run for longer at lower flow temperatures and hold the house at a steady temperature all day. In a well-insulated home that feels noticeably more comfortable; in a leaky solid-wall Victorian terrace it can feel underwhelming until the fabric is improved. This is why the heat-pump readiness of the house matters more than the brand of unit.
Carbon and the ten-year picture
Burning a therm of gas emits about 0.18 kgCO2 per kWh delivered. UK grid electricity in 2025 was around 0.21 kgCO2 per kWh; divided by a COP of 3.5 that is 0.06 kgCO2 per kWh delivered, roughly a third of the gas equivalent. The gap widens every year as the grid decarbonises further. A boiler fitted in 2026 will run for 12–15 years; its lifetime emissions are largely locked in on the day it is commissioned.
Which homes suit each, honestly
A gas boiler still makes sense in solid-wall properties without insulation upgrades planned, in flats without an outdoor unit location, and where the owner is likely to move within five years. A heat pump makes sense in cavity-wall or better fabric, in any home where the radiators are already reasonably sized, in properties with room for an outdoor unit within reasonable pipe length, and for anyone planning to stay long enough to benefit from grants and lower lifetime running costs. Hybrids exist but rarely earn their extra complexity in a domestic setting.
- You should probably fit a gas boiler if...
the existing one has died, the fabric is uninsulated and staying that way, you are moving within five years, or you live in a flat without a viable condenser location.
- You should probably fit a heat pump if...
your fabric is cavity-wall or better, your radiators are already generously sized, you have somewhere sensible for the outdoor unit, and you plan to stay long enough to feel the running-cost payback on a heat-pump tariff.
- It is genuinely close if...
you are between fabric upgrades and want to future-proof, or your gas boiler still works and the question is what to fit next time. In that case the honest answer is often 'insulate first, decide in three years'.
Heat pump vs gas boiler; typical UK three-bed semi (2026)
| Install cost, gas combi (like-for-like) | £2,200 – £3,500 |
| Install cost, air source heat pump (after £7,500 grant) | £3,500 – £7,500 |
| Annual running cost, gas combi | £560 – £720 |
| Annual running cost, heat pump on flat tariff | £720 – £860 |
| Annual running cost, heat pump on heat-pump tariff | £430 – £540 |
| Annual CO2 emissions, gas combi | ≈ 1,800 kg |
| Annual CO2 emissions, heat pump | ≈ 600 kg (and falling) |
Figures for a typical three-bed semi drawing ~10,000 kWh of heat per year. Sources: Ofgem cap Q1 2026, MCS installer data, Ofgem grid intensity 2025.
See what installers in your area would actually charge.
Join the installer waitlistFrequently asked questions
Is a heat pump cheaper to run than a gas boiler in the UK?+
On a standard flat electricity tariff, usually not; the gas boiler still costs slightly less. On a genuine heat-pump time-of-use tariff (Cosy Octopus, Ovo Heat Pump Plus and similar), a well-designed heat pump is meaningfully cheaper. The tariff choice is doing more work than the technology in this comparison.
Do I need new radiators for a heat pump?+
Sometimes, not always. Heat pumps run at flow temperatures of 35–50°C rather than the 65–75°C typical of gas systems, so radiators need more surface area to deliver the same heat. Many UK homes already have oversized radiators from decades of overspecified boilers; a good MCS designer will tell you which rooms need upsizing and which do not.
Can I keep the gas boiler as backup?+
You can, in a hybrid setup, but they rarely pay back the extra complexity in a domestic home. Most MCS designs now aim for a fully sized heat pump with immersion backup in the hot water cylinder rather than a hybrid; simpler to maintain and fully grant-eligible.
How long does a heat pump last?+
Modern inverter-driven monobloc units are designed for 15–20 years; broadly comparable to a well-serviced gas boiler. The bigger long-term difference is in refrigerant regulations and grid tariffs, both of which favour heat pumps over that horizon.
What if I am replacing a broken boiler tomorrow?+
A gas replacement is almost always the pragmatic answer; heat-pump surveys and MCS installs run to weeks, not days. The honest advice is to fit the replacement boiler, use the next few years to insulate and upgrade radiators, and price a heat pump properly when the boiler nears end of life.