Heat Pump vs Gas Boiler — Honest Comparison for UK Homes

Heat pumps use electricity. Gas boilers use gas. In the UK, electricity costs roughly 3–4 times more per unit (kWh) than gas. This is the central challenge that heat pump advocates often gloss over.

The saving grace is the Coefficient of Performance (COP). A heat pump doesn't generate heat — it moves it. For every unit of electricity it uses, it delivers 3 to 4 units of heat into your home. A gas boiler, even a modern condensing one, converts about 0.9 units of energy into heat per unit burned.

The maths works out roughly as follows at 2026 energy prices:

• Gas boiler: ~7p per kWh of heat delivered (gas at 6.4p, 90% efficiency)
• Heat pump (COP 3.0): ~8p per kWh of heat delivered (electricity at 24p)
• Heat pump (COP 3.5): ~7p per kWh of heat delivered
• Heat pump (COP 4.0): ~6p per kWh of heat delivered

At a COP of 3.0 — typical for a heat pump installed in a moderately insulated home running at slightly elevated flow temperatures — running costs are roughly comparable to gas. At a COP of 3.5 or above — achievable in a well-insulated home with properly sized radiators — running costs are lower than gas. The better your home is insulated, the better the economics.

There is a long-term tailwind too: the government has committed to reducing the electricity-to-gas price ratio as part of its net zero strategy, which would shift the economics further in heat pumps' favour over time.

This is where the gas boiler wins decisively, even after the BUS grant:

• New gas boiler (combi): £1,500–£3,500 installed
• Air source heat pump: £8,000–£15,000 installed, minus £7,500 BUS grant = £500–£7,500 net
• Ground source heat pump: £15,000–£35,000 installed, minus £7,500 BUS grant = £7,500–£27,500 net

Additionally, many homes need associated works: radiator upgrades, a new hot water cylinder, and sometimes electrical upgrades. These can add £2,000–£5,000 to the project. See our full cost guide for a detailed breakdown.

A heat pump powered by the UK electricity grid produces significantly fewer carbon emissions than a gas boiler — even today. The UK grid's carbon intensity has fallen dramatically over the past decade as coal has been phased out and renewables have expanded.

Current estimates put grid electricity at roughly 150–200g CO2 per kWh, against gas at about 204g CO2 per kWh. Factor in the heat pump's COP of 3x and the carbon per unit of heat delivered is roughly three times lower than gas. As the grid continues to decarbonise, this advantage will only grow.

Heat pumps heat differently from gas boilers, and this surprises some homeowners. A gas boiler typically fires up, heats water to 65–75°C, and blasts heat into your home quickly. A heat pump runs at lower temperatures — typically 35–45°C flow temperature — for longer periods, often continuously during cold weather.

The result is a home that stays at a more consistent temperature throughout the day, rather than heating up and cooling down in cycles. Many people find this more comfortable. However, it requires a change in how you use your heating: you can't quickly blast heat into a cold room the way you can with a gas boiler.

Heat pumps also perform well for hot water, though they typically heat water more slowly. Most installations include a hot water cylinder (tank) rather than the instant hot water you get from a combi boiler.

A heat pump has an outdoor unit — a fan and compressor unit about the size of a large suitcase — that runs outdoors. Modern units are quiet: typically 40–50 dB at one metre, which is about the same as a quiet conversation or a refrigerator. However, they run for long periods, sometimes overnight in winter, which can be noticeable depending on where the unit is sited.

Permitted development rules require the unit to be at least one metre from a property boundary, and you should consider neighbour proximity when deciding on placement. See our suitability guide for planning rules.

Be honest with yourself here. A heat pump is the wrong choice for some homes right now:

• Very poorly insulated homes — if your walls are uninsulated solid brick and your loft has no insulation, the heat demand will be too high for a heat pump to run economically. Fix the insulation first.
• Undersized radiators — if your home was designed for a high-temperature boiler and the radiators are small, you'll need to upgrade them for a heat pump to work well. This adds cost.
• No space for a cylinder — most heat pump installations require a hot water cylinder. If you're in a flat or small terrace with genuinely no space, the project becomes much harder.
• No outdoor space — you need somewhere to mount the external unit that meets the permitted development rules. Urban terraces with tiny rear yards can struggle.
• Short-term stay — the payback period is long enough that if you're planning to sell in under five years, the economics are harder to justify.

A heat pump is likely a good choice if:

• Your home is reasonably well insulated (cavity walls filled, loft insulated to 270mm)
• You have underfloor heating or room to upgrade radiators
• You're on oil or LPG — the economics are far stronger than against mains gas, often saving £500–£800 per year
• Your existing boiler is at end of life and you're about to replace it anyway
• You plan to stay in the property for 10+ years
• You care about reducing your carbon footprint

Off-gas-grid properties — those on oil, LPG, or electric storage heaters — almost always see better economics from a heat pump than mains gas users. If you're currently paying 8–9p/kWh for oil heat, a heat pump running at the same cost per unit of heat delivered is already a win on running costs, before the carbon benefits.