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Heat Pump vs Gas Boiler — UK Costs
Compare air source heat pumps with gas boilers for UK homes, covering running costs, BUS grant, carbon emissions and radiator sizing implications.
Side-by-Side Comparison
| Feature | Air Source Heat Pump | Gas Combi Boiler |
|---|---|---|
| Install cost | £8,000-14,000 (£500-6,500 after BUS) | £2,500-4,000 |
| Efficiency | COP 2.5-4.0 (250-400%) | 89-94% ErP |
| Annual running cost (3-bed) | £700-1,000 | £700-1,000 |
| CO2 per kWh heat | ~45g (at COP 3.0) | ~200g |
| Flow temperature | 35-55°C (most efficient at 35-45°C) | 60-80°C |
| Hot water | Needs cylinder (150-250L) | Instant (combi) or cylinder |
| Lifespan | 20-25 years | 12-15 years |
| Grant available | BUS £7,500 | None |
When to Choose a Heat Pump
- Well-insulated property (EPC C or better ideal)
- Underfloor heating installed or planned
- Eligible for the £7,500 BUS grant
- Off-gas properties (replacing oil or LPG)
- You want to future-proof against gas phase-out
- Solar PV installed to offset electricity costs
When a Gas Boiler Is More Practical
- Poorly insulated property not suitable for low-temperature heating
- Very limited outdoor space for the heat pump unit
- Tight budget and no BUS grant eligibility
- High hot water demand where instant combi delivery is preferred
Related Calculators
Use the Heat Pump Sizing Calculator to size a heat pump, or the Boiler Size Calculator for gas boiler sizing.
Next up: related pages
How We Calculate This
Frequently Asked Questions
It depends on the COP achieved and energy prices. At a COP of 3.0, a heat pump produces 3 kWh of heat per 1 kWh of electricity. With electricity at 26.11p/kWh and gas at 7.33p/kWh (Ofgem Q3 2026), the effective cost per kWh of heat is 8.7p (heat pump) vs 8.1p (90% efficient gas boiler). With an economy tariff or solar PV, heat pumps become clearly cheaper. Running costs are broadly similar for most homes.
The Boiler Upgrade Scheme (BUS) provides £7,500 towards an air-source or ground-source heat pump, and £5,000 towards a biomass boiler (biomass is further restricted to rural, off-gas-grid properties). The grant is claimed by your MCS-certified installer and deducted from the quote. Eligibility: the property must have a valid EPC with no outstanding loft/cavity insulation recommendations (unless exempt), an MCS-certified installer, and you must be replacing a fossil-fuel heating system. Properties on mains gas ARE eligible for heat pumps — BUS has no off-gas-grid requirement for ASHP/GSHP (that is HUG2). The scheme is funded to March 2030.
Usually yes. Heat pumps run most efficiently at lower flow temperatures (35-45°C vs 60-75°C for gas boilers). At 45°C flow, radiators produce roughly 50-60% of their rated output, so you may need to upsize some radiators or add additional ones. Properties with underfloor heating are ideal for heat pumps as UFH works well at low temperatures.
A gas combi boiler replacement costs £2,500-4,000 installed. An air source heat pump costs £8,000-14,000 installed before the BUS grant, or £500-6,500 after the £7,500 grant. Ground source heat pumps cost £15,000-25,000 before grants. The heat pump cost includes the outdoor unit, cylinder, controls and any radiator upgrades.
The UK electricity grid carbon intensity is around 136g CO2/kWh (DESNZ 2024 GHG conversion factors). At COP 3.0, a heat pump produces about 45g CO2 per kWh of heat. A gas boiler produces approximately 200g CO2/kWh of heat (natural gas 183g/kWh ÷ 92% efficiency per DESNZ 2024). Heat pumps cut heating carbon emissions by roughly 75%, and this improves as the grid decarbonises further.
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Last updated: July 2026
Verified against UK standards · estimates only, confirm with your supplier.