Ground source heat pumps (GSHP)

Ground source heat pumps extract heat from pipes buried in your garden or in vertical boreholes. The ground stays warmer than the air through winter, so a GSHP runs at higher efficiency than an air source unit, but the install is more disruptive and significantly more expensive.

How it works

Ground temperature in the UK sits stable at around 10 – 12 °C a few metres below the surface, year-round. A GSHP circulates a water/glycol mix through buried pipes (the "ground array"), absorbs that low-grade heat, and concentrates it via a compressor into your heating system, same thermodynamic cycle as an air source unit, just a more consistent heat source.

The ground array comes in two forms:

• Horizontal collector. Pipes laid in trenches 1 – 2 m deep, covering 2 – 3 times the floor area of the property. Requires substantial garden space and ground that can be dug.
• Vertical boreholes. 80 – 150 m deep, drilled by specialist rigs. Less surface area needed, but boreholes add £8,000 – £15,000 to the cost.

Benefits

• Highest year-round SCOP. Ground temperature stays consistent, so the heat pump doesn't lose efficiency on the coldest days the way an ASHP does. Expect SCOP 4.0+ in well-designed installs.
• Lower running costs over time. The SCOP advantage compounds over 20+ years, running costs can be 20 – 30% lower than an equivalent ASHP install.
• No outdoor unit. The heat pump itself sits indoors (utility room, garage). No outdoor box, no aesthetic concerns, no wind noise.
• Eligible for the £7,500 BUS grant in England and Wales, same as ASHPs.
• Very long ground-loop lifespan. Plastic ground pipes last 50+ years. You'll replace the heat pump itself once over the building's lifetime; the loop stays.
• Cooling potential. Some GSHPs can do passive cooling in summer by circulating cool ground water, minimal extra electricity cost.
• Quiet. The compressor lives indoors; outside there's nothing to hear.

Disadvantages

• Up-front cost is dramatic. Even after BUS, you're looking at £10,500 – £27,500. The borehole rigs are the single biggest cost variable.
• Requires significant garden access. Horizontal needs 2 – 3× the floor area in dig-able ground with no tree roots, no septic tank, no underground utilities. Vertical needs rig access (4 m clearance overhead, hard standing for the rig).
• Heavy disruption during install. Trenching turns your garden into a building site for a week. Borehole rigs are noisy and produce mud slurry; expect to landscape afterwards.
• Smaller installer pool. Many MCS-certified heat pump installers do air source only. Ground source needs specialist drilling subcontractors.
• Permits for boreholes. In some areas, deep boreholes need Environment Agency notification (UK aquifer protection rules). Your installer should manage this, but it adds weeks.
• Slow payback. The capital cost premium over ASHP rarely pays back in running costs within 15 years. The case is strongest when ASHP isn't practical (heritage site, no outdoor wall) or when boreholes can be combined with other ground works.
• Site-specific feasibility. Some sites can't host either array, solid rock under the topsoil, archaeological constraints, ground contamination. A geotechnical survey may be needed.

Best for

• Larger rural detached homes with substantial grounds.
• New-builds where ground works are already happening (groundworks contractor can dig trenches at marginal extra cost).
• Properties where an outdoor air-source unit is impractical (heritage frontage, conservation area restrictions).
• Owners with a 20+ year horizon and budget for premium install costs.
• Properties combining ground source with solar PV + battery for maximum self-generation.

Less suited to

• Urban homes with small or no garden.
• Terraced properties with shared garden boundaries.
• Sites with shallow bedrock or restricted access for drilling rigs.
• Owners with sub-15-year horizons who'd see better value from an ASHP install.

Ground array choice in detail

Horizontal collector

Cheaper option (£3,000 – £6,000 for pipes + trenching) but needs a lot of space. As a rough rule: a 6 kW heat pump needs 240 – 300 m² of usable horizontal ground area. Pipes are 1.2 – 2 m deep so they're below the seasonal frost line.

Vertical boreholes

£8,000 – £15,000 for a single 100 m borehole; £15,000 – £25,000 for two. Borehole spacing matters (5 m+ apart) to avoid thermal cross-talk. Total ground-loop cost can equal the heat pump itself.

Slinky / coiled collectors

Compressed-footprint horizontal collectors using slinky-shaped pipe coils, about 30 – 50% less trench length than straight pipes. Useful for marginal garden sizes; slightly lower performance than straight horizontal but cheaper than going vertical.

Real-world considerations

Disturbance during install

For horizontal: trenches 30 – 60 cm wide, 1.2 – 2 m deep, snaking across the lawn. Soil heaps are managed by the contractor but lawn rebuilds itself slowly (~6 months to look normal).

For boreholes: a truck-mounted rig drills each hole over 1 – 3 days. Loud during drilling. Drilling produces slurry that needs containing.

Heating distribution

GSHPs work best with low-temperature systems: underfloor heating or oversized radiators. They struggle with old microbore radiator systems unless those are also upgraded.

Hot water

Same constraint as ASHP: you need a stored cylinder (typically 200 – 300 L). Higher-output GSHPs heat the cylinder faster but the steady-state principle is the same.

FAQs

Will a GSHP work in clay soil?

Yes. Clay actually has decent thermal conductivity. Sandy or rocky soils need more pipe length to compensate for lower conductivity. Your installer's design calculations should account for soil type.

Can I put the ground loop under a driveway?

Technically possible but rarely sensible, driveways concentrate heat (good for thermal performance) but make future maintenance impossible. Stick to garden ground.

Does the loop affect the garden?

Once installed and re-turfed, you wouldn't know it was there. Plant roots above are fine (most don't go below 1 m). Avoid planting deep-rooted trees directly over the loop, as roots could damage pipes over decades.

What if I sell the house?

Ground source typically adds to property value as a recognised renewable heating system. Some surveys flag the GSHP as a positive EPC factor; selling agents are generally familiar by 2026.

Land ownership and shared boreholes

GSHP installs need the ground array to sit within land you own or have a documented legal right to disturb. For semi-detached or terraced properties with a shared garden boundary, get written agreement from neighbours before a survey proceeds, not after, some installers will refuse to quote without it. A small number of new developments and estates install shared ground arrays serving multiple properties from a single borehole field, which spreads the drilling cost but requires a management agreement covering maintenance access and cost-sharing if a fault develops.

If you're on a mortgage, tell your lender before groundworks start, most don't object to a GSHP install but some require notification for significant land disturbance, and it's better to check than assume. Boreholes deeper than roughly 50m in some areas may also need a screening check against the British Geological Survey's aquifer maps, your installer should handle this as part of the permitting process, but it's worth asking early rather than discovering a delay partway through.

Worked example: a rural farmhouse conversion

A five-bedroom farmhouse with a large garden and no mains gas has a heat loss of roughly 14 kW. Horizontal collector trenches covering 320 m² of the paddock, plus a 16 kW heat pump and cylinder, come to £24,000. After the £7,500 BUS grant, the net cost is £16,500. Running on an oil boiler previously cost around £2,400 a year; on a heat-pump tariff with a SCOP of 4.2, the GSHP runs at roughly £1,050 a year for the same heat demand, a saving that pays back the capital premium over an ASHP quote within about 12 years, faster than most retrofits because the property was off mains gas to begin with.

Compare with other types

Air source (ASHP) · Water source (WSHP) · Hybrid · Exhaust air (EAHP)

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