Key facts at a glance
- Average cost: £10,000-15,000 installed (before BUS grant)
- BUS grant: £7,500 towards installation. Your cost: £2,500-7,500
- Running costs: £800-1,200/year for a typical 3-bed semi (vs £900-1,400 for gas)
- COP (efficiency): 2.5-4.0, 1kW electricity produces 2.5-4kW of heat
- Lifespan: 15-20 years for outdoor unit, 25+ years for indoor components
- Best suited for: Well-insulated homes with adequate radiator sizing or underfloor heating
The short answer
An air source heat pump costs £10,000–£15,000 installed, and the £7,500 Boiler Upgrade Scheme grant brings that down to £2,500–£7,500 out of pocket. Running costs are £800–£1,200 a year for a typical 3-bed semi, against £900–£1,400 on gas.
The reason is efficiency: a COP of 2.5–4.0 means one unit of electricity delivers two and a half to four units of heat. The outdoor unit lasts 15–20 years. It works best in a well-insulated home with radiators sized for 35–45°C flow temperatures or underfloor heating.
How air source heat pumps work
An air source heat pump (ASHP) extracts heat from outside air, even when it’s cold, and transfers it into your home. It works like a fridge in reverse:
- The outdoor unit draws air over a heat exchanger containing a cold refrigerant
- The refrigerant absorbs heat from the air and evaporates (even at -15°C, there’s usable heat)
- A compressor increases the refrigerant’s temperature
- The hot refrigerant passes through a condenser, transferring heat to your central heating
- The refrigerant cools, condenses, and the cycle repeats
The key metric is the Coefficient of Performance (COP), how many units of heat per unit of electricity. A COP of 3.0 means 1kW of electricity produces 3kW of heat. UK heat pumps typically achieve 2.5-4.0 depending on outside temperature and system design.
Real costs breakdown
| Component | Cost Range | Notes |
|---|---|---|
| Heat pump unit | £3,000-6,000 | 5-16kW capacity |
| Installation labour | £3,000-5,000 | Typically 2-3 days |
| Hot water cylinder | £1,000-2,000 | Required if you don’t have one |
| Radiator upgrades | £500-3,000 | May need upsizing for lower temps |
| Electrical work | £300-800 | Dedicated circuit, possible CU upgrade |
| Total installed | £8,000-15,000 | After BUS grant: £500-7,500 |
Boiler Upgrade Scheme (BUS), £7,500 grant
The BUS provides £7,500 towards air source heat pump installation. Your MCS-certified installer applies on your behalf. Available in England and Wales with a valid EPC. Check if you qualify →
Running costs vs gas boilers
At current UK energy prices, a well-designed heat pump system (COP 3.0+) is slightly cheaper to run than gas. A poorly designed system (COP below 2.5) can cost more. Installation quality matters enormously.
| Scenario | Gas Boiler | Heat Pump (COP 3.0) | Heat Pump (COP 2.5) |
|---|---|---|---|
| Annual heat demand | 12,000 kWh | 12,000 kWh | 12,000 kWh |
| Energy needed | 15,000 kWh gas | 4,000 kWh elec | 4,800 kWh elec |
| Unit cost | 7.33p/kWh | 26.11p/kWh | 26.11p/kWh |
| Annual cost | £1,100 | £1,044 | £1,253 |
Is a heat pump right for your home?
Heat pumps work best when these criteria are met:
- Good insulation, loft insulation, double glazing, and draught-proofing are essential. Heat pumps work at 35-45°C vs 60-70°C for gas, so your home needs to retain heat well
- Adequate radiators. You may need larger radiators or underfloor heating
- Outdoor space, ~1m² with good airflow, away from bedroom windows (40-60dB noise)
- Hot water cylinder. Required. If you have a combi boiler, you’ll need to install one, and an existing boiler cylinder usually has too small a coil to reuse — see heat pump cylinder sizing
- Electrical capacity, dedicated circuit needed. Older homes may need a consumer unit upgrade
When a heat pump may NOT be right
If your home has poor insulation (solid walls, single glazing, no loft insulation), invest in insulation first. A heat pump in a poorly insulated home runs at higher temps, reducing COP and increasing bills. ECO4 may fund insulation for eligible households.
Noise considerations
Modern heat pumps produce 40-60dB, similar to a quiet conversation. UK Permitted Development requires the unit to be 1m+ from your property boundary. If near a bedroom window, discuss placement with your installer.
Installation process
A typical installation takes 2-3 days:
- Day 1: Outdoor unit on concrete base, refrigerant pipework run
- Day 2: Hot water cylinder installed, heating connected, electrical work
- Day 3 (if needed): Radiator upgrades, system balancing, commissioning
Maintenance
- Annual service: £100-200. Check refrigerant, clean filters, inspect electricals
- Keep outdoor unit clear: Remove leaves and debris, maintain airflow
- Defrost cycles: Normal in cold weather. You may see steam, this is fine
- No annual gas safety check required (one less hassle vs gas boilers)
When something does go wrong, it is usually one of a handful of things: bills higher than expected because the flow temperature was set too high, a house that never quite reaches target, or fan noise. Causes and fixes are in common air source heat pump problems.
Frequently asked questions
Do heat pumps work in cold UK weather?
Yes. Modern heat pumps work down to -15°C or lower. UK rarely drops below -5°C. COP decreases in cold weather (from ~3.5 at 7°C to ~2.5 at -5°C) but still generates more heat than electricity consumed.
How long does a heat pump last?
Outdoor unit: 15-20 years. Indoor components: 25+ years. Comparable to or longer than gas boilers (10-15 years).
Can I keep my gas boiler as backup?
Yes, hybrid systems use a heat pump for most heating and gas for peak demand. However, hybrid systems don’t qualify for the BUS grant.
Do I need planning permission?
No. Heat pumps are Permitted Development in England and Wales. Listed buildings and conservation areas may need consent.