Heat Pump vs Gas Boiler UK — Which Is Right For You?

How Each Works

Gas Boilers

A gas boiler burns natural gas (or LPG) to heat water, which is then sent to your radiators and, in a combi or system setup, to your taps and showers. The boiler typically runs at high flow temperatures (e.g. 60–75 °C), so existing radiators often work without changes. Gas has been the default for UK central heating for decades: installs are well understood, and the fuel has historically been relatively cheap. Boilers are efficient—modern condensing models can exceed 90% efficiency—but they still produce carbon emissions at the point of use and depend on fossil fuel.

Heat Pumps

A heat pump doesn't burn fuel. It uses electricity to move heat from the outside air (air-source) or the ground (ground-source) into your home. For every unit of electricity used, a good heat pump can deliver several units of heat, so the "efficiency" (coefficient of performance, or COP) can be 3 or more. Heat pumps work best with lower flow temperatures (e.g. 35–50 °C), so they often pair with larger radiators, underfloor heating, or both. They need a well-insulated home and careful sizing. In return, they can slash carbon emissions and, depending on electricity prices, reduce running costs compared to gas.

Running Costs Comparison

Running costs depend on your tariff, insulation, and how you use heating. When gas was much cheaper than electricity per unit of energy, gas boilers were usually cheaper to run. In recent years, gas prices have risen and electricity prices have been more variable; with a heat pump's high COP, the gap has narrowed and in some cases reversed.

A typical comparison: if gas is around 7p/kWh and electricity 27p/kWh, a 90% efficient boiler uses about 11 kWh of gas to deliver 10 kWh of heat. A heat pump with a COP of 3 uses about 3.3 kWh of electricity for the same 10 kWh of heat. So the boiler might cost roughly 77p for that heat, and the heat pump about 89p—close. If electricity is cheaper (e.g. on an off-peak or heat pump tariff) or gas is dearer, the heat pump can win. The only way to know for your home is to use current local prices and a proper heat loss figure. Well-insulated homes with low-temperature systems get the best results from a heat pump.

Upfront Costs

A gas boiler replacement—combi or system—typically costs in the region of £1,500–£3,500 including installation for an average home, depending on the model and complexity. It's a well-established product with plenty of installers and competition.

A heat pump installation is usually more expensive. An air-source heat pump system—including the unit, hot water cylinder, possible radiator or emitter upgrades, and commissioning—might be £10,000–£18,000 or more before grants. Ground-source heat pumps cost more because of the ground loop. The Boiler Upgrade Scheme (BUS) grant of up to £7,500 significantly reduces the net cost of an air-source or ground-source heat pump in England and Wales, which we cover below. Even with the grant, the outlay is often higher than a boiler, so the payback depends on running cost savings and how long you stay in the property.

Environmental Impact

Gas boilers produce carbon dioxide when they burn gas. Even an efficient condensing boiler emits around 2–2.5 kg CO₂ per kWh of heat (depending on exact efficiency). The UK grid is decarbonising, so electricity used by a heat pump is increasingly from low-carbon sources. Per kWh of heat delivered, a heat pump can have less than half the carbon footprint of a gas boiler, and that gap will widen as the grid gets greener.

If reducing your home's carbon emissions is a priority, a heat pump is the stronger choice. Gas will remain in the mix for years, but policy is moving away from new gas heating in the long term. Choosing a heat pump now future-proofs your property and can improve its appeal to buyers who care about energy and sustainability.

Suitability by Property Type

Well-insulated, modern homes: Heat pumps work very well. Low heat loss means a smaller heat pump and lower flow temperatures, so radiators or underfloor heating can be sized to work efficiently. New builds and recently refurbished homes are ideal candidates.

Older, less insulated homes: A heat pump can still work, but the heat loss is higher. You may need a larger unit, higher flow temperatures, and more radiator or emitter upgrades. Running costs can be higher than in a well-insulated house. Many installers and the BUS scheme encourage "fabric first" improvements (insulation, glazing) before or alongside a heat pump to get the best result. A gas boiler remains a practical option if you're not ready to invest in insulation and emitter upgrades.

Flats and small homes: Air-source heat pumps can be installed in flats where there is space for an outdoor unit (e.g. balcony or communal area) and often a cylinder. Gas may still be the default where a gas supply exists and space is tight. Each property is different; an MCS installer can advise on feasibility.

The £7,500 Boiler Upgrade Scheme (BUS) Grant

In England and Wales, the Boiler Upgrade Scheme offers a grant of up to £7,500 towards the cost of an eligible air-source or ground-source heat pump installation. The grant is paid to the installer, who passes the saving on to you, so the amount you pay is the quoted price minus the grant. To qualify, you usually need to own your home (or have landlord consent), replace an existing fossil fuel heating system, and use an MCS-certified installer who will carry out the work to the scheme's standards.

The BUS grant makes a heat pump much more affordable. A system that might cost £14,000 could drop to £6,500 after the grant, bringing it closer to the total cost of a premium boiler plus cylinder. Funding is limited and applied for on a first-come, first-served basis, so check current availability on the official BUS pages. Scotland and Northern Ireland run separate schemes—check what support is available in your region.

Next Steps

Weigh running costs, upfront cost (including BUS if you qualify), and environmental impact against your property and plans. Use our heat pump size calculator to get a ballpark kW range, then get quotes from both gas boiler and MCS heat pump installers. Ask for a heat loss survey if you're serious about a heat pump—it will tell you the exact size and whether your radiators need upgrading. Whether you choose a heat pump or a gas boiler, a well-sized system and a good installer will keep you comfortable for years to come.