Ground Source vs Air Source Heat Pump: Which Is Best?

Air source heat pumps are significantly cheaper to install. A typical 8–12kW ASHP installed costs £8,000–£13,000 before the £7,500 BUS grant (net cost £500–£5,500). A ground source heat pump including boreholes or ground loops costs £20,000–£45,000 depending on ground conditions and loop type — substantially more even after the £7,500 BUS grant.

Ground source heat pumps are typically more efficient than air source, because the ground maintains a stable temperature of 8–12°C year-round, whereas air temperature drops in winter when heating demand is highest. A GSHP achieves SCOP 4.0–5.0 (400–500% efficiency). A modern ASHP achieves SCOP 3.2–4.5 — still far more efficient than a gas boiler (80–90%) but lower than GSHP at peak demand.

Yes. The Boiler Upgrade Scheme grant of £7,500 applies to both air source and ground source heat pumps. Ground source heat pumps were previously eligible for £6,000, but the grant was equalised to £7,500 in 2023. To claim the grant, the installation must be carried out by an MCS-certified installer and the property must have an EPC rating of D or above (E–G ratings may require efficiency improvements first).

For a horizontal ground loop system, you need a garden area approximately 2–3 times the floor area of your home. A 3-bed house needing a 6kW system typically requires 200–600m² of suitable ground — approximately 0.06 acres. For properties with smaller gardens, vertical boreholes are an alternative: typically 2–4 boreholes of 100m depth, each requiring a drilling pad of approximately 5m². Boreholes cost more but require less land area.

Ground source is particularly well-suited to rural East Anglia properties with large gardens or farmland. Norfolk and Suffolk have extensive agricultural land, flat topography (easier drilling), and many larger period properties that benefit from the higher efficiency of GSHP. For a Suffolk farmhouse or converted barn with half an acre or more, a GSHP with horizontal ground loops is a very viable option.

Ground source heat pumps are significantly quieter than air source, because there is no outdoor fan unit — the heat extraction from the ground loop is silent. The only noise comes from the compressor unit inside the property, typically in a plant room or utility room, producing 40–45 dB(A). There are no planning or permitted development noise constraints for GSHP equivalent to the 42 dB outdoor rule for ASHP.

For a Cambridge terrace with a small rear garden, air source is the practical choice. Terraced houses typically lack the garden area for a horizontal ground loop, and drilling vertical boreholes in an urban terrace setting is expensive and logistically complex. A modern air source heat pump (Daikin Altherma, Vaillant arotherm+) can be mounted on the rear wall, well within the 42 dB permitted development limit.

The same considerations apply as for air source — the heat pump's flow temperature (35–55°C) determines whether existing radiators are adequately sized. Ground source heat pumps can typically achieve slightly lower flow temperatures due to higher ground temperatures, but may still require some radiator upgrades. The best option for both GSHP and ASHP is underfloor heating at 35°C, which matches the optimal flow temperature exactly.