For many UK homeowners, the real decision is no longer just whether the old boiler can survive another winter. It is whether to replace it with another gas boiler or switch to a heat pump. That comparison matters because the two systems work differently, cost different amounts upfront, and sit on opposite sides of the UK's long-term plan to decarbonise home heating.
A gas boiler is still the default replacement in many homes because it is familiar, relatively cheap to install, and works well with existing radiator systems. A heat pump, usually an air source heat pump, has a higher upfront cost but can cut emissions significantly and, in the right home, deliver competitive running costs too.
To compare them fairly, you need to look past slogans. Upfront price is only one part of the picture. The more useful questions are: how much heat does your home need, what are current fuel prices, how efficient will each system be in your property, and how long do you expect to stay in the home? This guide uses current UK reference points from Ofgem, Energy Saving Trust and GOV.UK to answer those questions in practical terms.
Heat pump vs gas boiler at a glance
If you want the short version, gas boilers usually win on upfront affordability and easy replacement. Heat pumps usually win on carbon, lifespan and access to grants. Running costs can go either way depending on the home's heat demand, the heat pump's seasonal performance and the tariff used.
| Factor | Air source heat pump | Gas boiler |
|---|---|---|
| Upfront cost | £8,000-£14,000 before grant; often £2,000-£6,000 after BUS | Roughly £2,000-£4,000 installed |
| Running cost | Can rival gas in efficient homes and on good tariffs; weaker if designed badly | Often competitive on current standard tariffs |
| Lifespan | 20 years or more is common | Typically 12-15 years |
| Maintenance | Annual check recommended; fewer combustion components | Annual boiler service strongly expected |
| Carbon emissions | Usually much lower overall because it uses less final energy | Higher emissions from direct fossil fuel combustion |
| Comfort | Steady low-temperature heat; may need larger radiators | Fast response and familiar high-temperature operation |
| Grants | Boiler Upgrade Scheme offers £7,500 in England and Wales | No equivalent mainstream replacement grant |
Upfront costs compared
On purchase price alone, a gas boiler is still much cheaper. A straightforward replacement gas combi or system boiler typically lands in the region of £2,000 to £4,000 installed, depending on brand, output, controls and how much pipework or flue work is needed. If the swap is genuinely like-for-like and the existing system is in decent shape, this is often the lowest-cost route back to reliable heating.
An air source heat pump is a different proposition. A realistic installed range for many UK homes is around £8,000 to £14,000 before grant support. GOV.UK confirms that the Boiler Upgrade Scheme currently provides £7,500 towards eligible air source and ground source heat pumps in England and Wales. That means many households end up paying something more like £2,000 to £6,000 net, though some properties still sit above that if they need cylinder changes, pipework alterations or radiator upgrades.
A ground source heat pump usually costs more again, often around £15,000 to £25,000 or beyond once boreholes or ground loops are included. It can deliver excellent performance, but for most mainstream retrofit projects the practical choice is between a gas boiler and an air source heat pump.
The main mistake here is comparing the cheapest boiler quote with the heat pump price before grant. The fairer comparison is the boiler replacement price against the net homeowner cost after BUS, plus a view on how long the system is likely to last.
Running costs: which is cheaper?
This is where the comparison becomes less obvious. Under Ofgem's price cap for 1 January to 31 March 2026, the benchmark direct-debit rates are 27.03p/kWh for electricity and 6.99p/kWh for gas. On unit price alone, gas looks dramatically cheaper. But a heat pump does not convert electricity to heat one-for-one. A well-performing system may deliver roughly three units of heat from one unit of electricity over the season.
Take a home needing 12,000kWh of useful heat in a year. A gas boiler operating at about 90% seasonal efficiency would need around 13,333kWh of gas. At 6.99p/kWh, that is about £932 per year for the fuel. A heat pump with a seasonal performance factor of 3.0 would use around 4,000kWh of electricity. At 27.03p/kWh, that is about £1,081 per year.
In that example, gas wins. But if the heat pump reaches a seasonal performance of 3.5, electricity use falls to about 3,429kWh, which works out at roughly £927 per year on the same tariff. Add a cheaper heat-pump-friendly tariff or some off-peak optimisation for hot water, and the heat pump can come out ahead. If the system only manages 2.5, though, annual cost rises to roughly £1,297 and gas is clearly cheaper.
So when does a heat pump win? Usually when the home is reasonably well insulated, the emitters allow lower flow temperatures, the installer has designed the system properly, and the household is on a sensible electricity tariff. When does gas win? Usually in homes that need higher flow temperatures, have weak insulation, or where the heat pump has been installed as a simple boiler substitute without enough design attention.
Energy Saving Trust is right to emphasise that running costs depend heavily on system design and fuel prices, not just the appliance itself. That is why generic statements like "heat pumps are always cheaper" or "gas is always cheaper" are both too blunt to be useful.
Maintenance and lifespan
A modern gas boiler typically lasts around 12 to 15 years in normal domestic use, though some fail earlier if maintenance is poor or the system water quality is bad. Annual servicing is routine, and homeowners are used to paying roughly £90 to £150 a year for that, sometimes more in London or where repairs are bundled into a care plan.
A heat pump usually has a longer expected service life, with 20 years or more often cited for the main unit when it is installed and maintained properly. Annual service or inspection costs vary, but a broad range of £150 to £300 is common depending on location, brand support and whether cylinder, filters and glycol circuits need attention.
The difference is not just years. Boilers contain combustion components, burners, flues and gas safety issues. Heat pumps have fans, compressors and refrigeration circuits, but they avoid direct on-site combustion. In broad terms, the heat pump can be seen as the longer-life asset, while the boiler is cheaper to buy but usually needs replacing sooner.
Carbon emissions comparison
This is the category where the heat pump usually has the clearest advantage. The current UK government greenhouse gas reporting conversion factors put natural gas at about 0.203kgCO₂e per kWh and grid electricity at about 0.207kgCO₂e per kWh. At first glance those numbers look surprisingly similar. But they are not used in the same way.
A gas boiler needs close to one kWh of gas input for each kWh of heat output, and more once efficiency losses are included. A heat pump may only need around a third as many kWh of delivered energy to provide the same heat. Using the earlier 12,000kWh heat demand example, the gas boiler might consume 13,333kWh of gas, producing about 2.7 tonnes of CO₂e. A heat pump with a seasonal performance of 3.0 would consume 4,000kWh of electricity, producing about 0.8 tonnes of CO₂e.
That is why heat pumps are central to UK heating policy even before the grid gets cleaner. And as the electricity system continues to decarbonise over time, the emissions advantage should widen further.
Comfort and practicality
A boiler and a heat pump heat homes in different ways. A gas boiler often runs at higher flow temperatures and gives a familiar burst of quick heat. A heat pump tends to work best when delivering steady lower-temperature heat over longer periods. That can feel different at first, but many households find the comfort more even once the system is properly dialled in.
The practical catch is that heat pumps usually need sufficient emitter area. In plain English, that may mean larger radiators or underfloor heating so rooms can stay warm without the system having to run excessively hot. They also need outdoor space for the external unit and produce some fan and compressor noise, though good siting and compliant installation normally keep that manageable.
Boilers are easier when space is tight and the home already has a conventional high-temperature radiator circuit. Heat pumps need more design thinking, and usually a hot-water cylinder if the property does not already have one. So the comfort question is not just "which is warmer?" but "which system suits the building and your expectations of how heating should behave?"
Grants and incentives
The grant landscape heavily favours heat pumps. In England and Wales, the Boiler Upgrade Scheme offers £7,500 for eligible air source and ground source heat pump installations. That is a major reason the upfront gap between a boiler and a heat pump is no longer as large as many homeowners assume.
There is no equivalent mainstream grant for replacing an old gas boiler with a new gas boiler. Some households may be eligible for other efficiency or local-authority support schemes depending on circumstances, but the national signal is clear: public funding is aimed at low-carbon heating, not at locking in another fossil fuel appliance for the next decade or more.
Which is right for your home?
For a well-insulated modern home, especially one with decent radiator sizing or underfloor heating, an air source heat pump is often the stronger long-term choice. It should be easier to run at low flow temperatures, emissions will be lower, and the Boiler Upgrade Scheme can make the upfront cost surprisingly competitive.
For an average semi-detached house, the answer depends on the design details. Many semis can take a heat pump successfully, but they may need one or two larger radiators, better controls and some fabric improvements. If the budget is very tight and the existing system is straightforward, a boiler replacement may still be the practical short-term answer.
For an older stone cottage or hard-to-treat property, the verdict is more conditional. A heat pump is not impossible, but the design margin is tighter. If insulation is weak and high flow temperatures are unavoidable, running costs may disappoint. In those cases, a high-quality boiler or a staged retrofit plan can still be the more realistic route until the property is upgraded.
The best decision is rarely ideological. It is about your home's heat loss, your budget, your appetite for improvement work and how long you plan to stay put.
Frequently asked questions
Is a heat pump cheaper to run than a gas boiler in the UK?
It can be, but it depends on the electricity tariff, gas tariff, the heat pump's seasonal efficiency and the home's heat demand. A well-designed heat pump operating at a seasonal performance of around 3 or better can get close to gas and sometimes beat it, while a poorly set-up one can cost more.
Is a heat pump more expensive to buy than a gas boiler?
Yes. A replacement gas boiler is usually the cheapest upfront option. In broad UK terms, an air source heat pump may cost about £8,000 to £14,000 before the Boiler Upgrade Scheme grant, while a gas boiler replacement often lands around £2,000 to £4,000 installed.
Do heat pumps emit less carbon than gas boilers?
Yes in normal UK use. Grid electricity and gas now have similar headline carbon factors per kWh, but a heat pump usually delivers around three units of heat from one unit of electricity. That means total emissions for the same amount of heat are typically much lower than burning gas directly.
Can I swap a gas boiler for a heat pump in an older house?
Often yes, but the home may need design work such as larger radiators, better controls or modest insulation improvements. Older properties are not automatically unsuitable, but they do need a proper room-by-room heat-loss assessment rather than a simple like-for-like appliance swap.
Is there a grant for replacing a gas boiler with another gas boiler?
No equivalent mainstream grant exists for replacing an old gas boiler with a new gas boiler in England and Wales. The main national support is the Boiler Upgrade Scheme, which offers £7,500 towards eligible air source and ground source heat pump installations.
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