Air Source vs Ground Source Heat Pump: Which Is Right for Your Home?

How Heat Pumps Work: The Common Principle

Both air source heat pumps (ASHPs) and ground source heat pumps (GSHPs) operate on the same thermodynamic principle: they move heat from one place to another rather than generating it by burning fuel. In winter, they extract heat from the outside environment (air or ground) and deliver it, amplified, into the home. This process is highly efficient — for every 1 kWh of electricity consumed, a well-designed heat pump system typically delivers 2.5–4 kWh of heat energy.

This efficiency ratio is called the Coefficient of Performance (COP). A higher COP means lower running costs for the same heat output. The key difference between ASHP and GSHP is the temperature of the heat source they draw from, which fundamentally affects efficiency and system design.

Air Source Heat Pumps (ASHP)

An ASHP extracts heat from outdoor air, even when temperatures are as low as -15°C. The unit is installed outside the property (typically wall-mounted or on a plinth) and connected to the home's heating system via refrigerant pipework.

**Advantages:**

• Lower installation cost (typically £8,000–£14,000 before grant)
• Simpler installation — no groundworks required
• Suitable for most UK properties with adequate outdoor space
• Eligible for the Boiler Upgrade Scheme (BUS) grant: £7,500 in 2026
• Can be installed in one to two days

**Disadvantages:**

• Efficiency varies with outdoor temperature — performance drops in very cold weather (though modern units cope well even at -5°C to -10°C)
• External unit produces some noise (typically 40–55 dB at 1 metre — comparable to a quiet conversation)
• Planning permission may be required in conservation areas or for listed buildings
• Requires space outside the property; not suitable for terraced houses with no side or rear access

**Typical COP:** 2.5–3.5 in UK winter conditions, rising to 3.5–5+ in spring and autumn

**Installed cost after BUS grant:** £500–£6,500 (varies significantly by property size, existing system, and heat distribution)

Ground Source Heat Pumps (GSHP)

A GSHP extracts heat from the ground, which maintains a relatively stable temperature of approximately 10–12°C year-round at depths below the frost line in the UK. A network of pipework (the "ground array") is buried in the garden or borehole-drilled vertically into the earth, circulating a water-antifreeze mixture that absorbs ground heat.

**Advantages:**

• More stable efficiency year-round due to consistent ground temperature
• Higher average COP (typically 3.5–5)
• Quieter — the main unit is installed inside the property
• Longer lifespan for the ground array (50+ years for horizontal loops; 25–50 years for boreholes)

**Disadvantages:**

• Significantly higher installation cost (typically £20,000–£45,000)
• Requires either: substantial garden area for horizontal loops (approximately 400–600m² for an average home), or vertical borehole drilling (£50–£100 per metre, typically 100–150m depth)
• Installation is disruptive — horizontal arrays require excavation of significant garden area
• Eligible for BUS grant: £7,500, but the absolute cost remains much higher
• Not suitable for properties without large gardens or borehole access

**Typical COP:** 3.5–5 year-round

**Installed cost after BUS grant:** £12,500–£37,500+

Which Is Right for Your Home?

For most UK residential properties, an air source heat pump is the practical choice. The lower cost, simpler installation, and sufficient performance in the UK climate make it suitable for the majority of properties. Ground source is most appropriate where: the property has a large garden with ground suitable for horizontal loops; the efficiency premium of GSHP is needed to make the economics stack up; or where planning restrictions prevent an external ASHP unit (rare).

Is Your Home Ready for a Heat Pump?

Heat pumps work best with well-insulated homes and low-temperature heat distribution systems. They deliver water at around 35–55°C (compared to a gas boiler's 65–80°C), which means:

• Underfloor heating is ideal (designed for low flow temperatures)
• Radiators may need to be upsized (larger radiators deliver more heat at lower temperatures)
• Good insulation is essential — a poorly insulated home will require a larger heat pump running longer hours, reducing efficiency gains

Before installing a heat pump, ensure your loft insulation is at least 270mm, cavity walls are filled (if applicable), and draught-proofing is in place. A heat pump installer should carry out a BS EN 12831 heat loss calculation for your property before specifying system size.

The Boiler Upgrade Scheme (BUS)

The government's Boiler Upgrade Scheme provides a £7,500 voucher towards the cost of installing an ASHP or GSHP. The scheme is administered by Ofgem. Installations must be carried out by a MCS-certified installer, and the property must have a current EPC with no outstanding recommendations for loft or cavity wall insulation. Check your property's EPC on Property Passport UK before applying — an outstanding insulation recommendation on the EPC can delay or complicate your BUS application.