The UK government's Boiler Upgrade Scheme pays £7,500 towards a qualifying air-source heat pump, paid directly to your installer. For most homes, this makes the out-of-pocket cost of a heat pump installation comparable to or less than a new gas boiler.
At a glance
| Air source heat pump ✓ | Gas boiler | |
|---|---|---|
| Upfront cost (supply + install) | £9,500–£14,000 | £1,500–£3,500 |
| After £7,500 BUS grant | £2,000–£6,500 ✓ | No grant available |
| Efficiency | 300–450% (COP 3–4.5) ✓ | 85–95% |
| Lifespan | 15–20 years ✓ | 10–15 years |
| Typical annual running cost* | £900–£1,500 | £1,000–£1,700 |
| Carbon emissions | Very low, and improving ✓ | High, locked in |
| Energy price exposure | Electricity (falling share) ✓ | Gas (rising historically) |
| Maintenance | Annual service, no Gas Safe cert | Annual Gas Safe cert required |
| Works with underfloor heating | Ideal ✓ | Yes |
| Works with existing radiators | Often yes (check sizing) | Yes |
| Future-proof | Yes, grid gets cleaner over time ✓ | Gas phase-out planned |
*Based on a typical 3-bed UK home at 2025 energy prices (electricity 28p/kWh, gas 7p/kWh). Heat pump costs shown with standard tariff, time-of-use tariffs (e.g. Octopus Cosy) reduce this further.
Upfront cost
A gas boiler replacement, supply and installation, typically costs £1,500–£3,500. A heat pump installation costs more: £7,000–£14,000 depending on the size of the unit, the complexity of the install, and whether your radiators need upgrading.
However, the UK government's Boiler Upgrade Scheme (BUS) provides a £7,500 grant towards a qualifying air-source heat pump installation. This grant is paid directly to your MCS-certified installer, reducing your upfront cost significantly. Many homeowners with an 8 kW heat pump will pay less out of pocket than a new gas boiler after the grant is applied.
Running costs
Gas is currently around 7p/kWh; electricity around 28p/kWh. But a heat pump produces 3–4.5 units of heat per unit of electricity, compared to less than one unit from a gas boiler. That efficiency gap closes the running cost difference significantly, and in well-insulated homes, the heat pump is already cheaper to run.
Gas 7p/kWh, electricity 28p/kWh. Does not include standing charges.
The key takeaway: a heat pump in a reasonably insulated home costs similar to or less than a gas boiler to run today. As gas prices have historically risen faster than electricity prices, and as the grid decarbonises (making electricity cheaper to produce), the heat pump advantage grows over time.
Switching to a time-of-use electricity tariff (such as Octopus Cosy or Agile) can further reduce running costs by running the heat pump during off-peak hours.
Efficiency: COP explained
A gas boiler burns gas and converts roughly 85–95% of it to heat, the rest goes up the flue. A heat pump does not burn anything. It moves heat from outdoor air into your home using a refrigerant circuit, and because it moves heat rather than generating it, it can produce 3–4.5 units of heat per unit of electricity consumed. This ratio is called the Coefficient of Performance (COP).
COP varies with outdoor temperature and flow temperature. It is highest on mild days (COP 4–5) and lowest on the coldest days (COP 2.5–3). The Seasonal COP (SCOP) averages performance across a heating season, in the UK, a modern inverter heat pump achieves SCOP 3.0–4.2 depending on the home.
The spec sheet COP is measured at A7/W35, 7 °C ambient, 35 °C flow temperature. This represents typical UK shoulder-season conditions, which is when most of your heating hours occur.
Installation
Installing a gas boiler is a one-day job for a Gas Safe engineer. Replacing an existing boiler like-for-like is the simplest domestic heating job there is.
A heat pump installation is more involved but typically still completed in 1–3 days. The outdoor unit is mounted on a wall bracket or ground slab. Pipework connects to your existing wet heating system. The main additional decisions are:
- Hot water cylinder. If you currently have a combi boiler, you will need a hot water cylinder (200–300 litres) fitted as part of the installation.
- Radiator check. Because heat pumps run at lower flow temperatures, your installer will check each radiator is large enough to deliver the required heat. Some may need upsizing.
- Electrical supply. Most domestic units run on 230 V single-phase; larger 14–16 kW units may need 400 V three-phase supply, which requires an electrician.
Environmental impact
A gas boiler burns a fossil fuel. Even a 95% efficient boiler emits roughly 215 g CO₂ per kWh of heat delivered. The UK electricity grid currently emits around 150–200 g CO₂/kWh, and this figure is falling as more renewable generation comes online. At a COP of 3.0, a heat pump emits around 50–65 g CO₂ per kWh of heat, roughly a 70% reduction in carbon emissions vs gas.
By 2030, as the grid further decarbonises, a heat pump installed today will be running on progressively cleaner electricity, the emissions reduction improves over its lifetime without any changes to the system.
The 15-year picture
Heat pumps last 15–20 years. Gas boilers typically need replacing after 10–12. Over a full product lifetime, the comparison shifts firmly in the heat pump's favour, you avoid one complete boiler replacement, and gas prices have historically risen faster than electricity.
| Heat pump | Gas boiler | |
|---|---|---|
| Upfront (after grant) | ~£3,500 | £2,800 |
| Replacement at year 12 | — | +£2,800 |
| Annual running (×15 years) | ~£15,000 | ~£16,500 |
| Total over 15 years | ~£18,500 ✓ | ~£22,100 |
| Carbon saved vs gas | ~70% reduction ✓ | Baseline |
Illustrative, based on 2025 energy prices, flat for simplicity. Standard electricity tariff used for heat pump; off-peak tariffs reduce this further.
Which should you choose?
Choose a heat pump if:
- Your home has loft insulation and double glazing
- You are replacing a boiler that is at end of life
- You want to reduce your carbon footprint
- You qualify for the £7,500 Boiler Upgrade Scheme grant
- You have or plan underfloor heating
- You are planning a long-term stay (15+ years to benefit from running cost savings)
A gas boiler may still make sense if:
- Your boiler is relatively new and still working well
- You are planning to sell in the short term and cannot recoup the upfront cost
- Your property has no suitable outdoor space for a unit
The bottom line
If your boiler needs replacing, the case for a heat pump is strong: after the £7,500 grant, the upfront cost difference is modest, running costs are comparable (and lower with an off-peak tariff), and you avoid a second boiler replacement in 10–12 years. Over 15 years, a heat pump is typically £3,000–£5,000 cheaper in total than the gas alternative, and produces around 70% less carbon.
The one caveat: your home's insulation quality matters. A heat pump in a well-insulated home (loft insulation, double glazing) runs efficiently and cheaply. In a poorly insulated property, improving the fabric first gets you a smaller unit, lower running costs, and an easier path to grant eligibility.
Ready to explore heat pumps for your home?
Browse the Thermotec range or check your eligibility for the £7,500 grant.