Home Heat Pump Guide

Air Source vs Ground Source Heat Pump: Complete UK Comparison

If you have decided that a heat pump is right for your home, the next question is which type. The two main options — air source heat pumps (ASHPs) and ground source heat pumps (GSHPs) — both extract renewable heat from the environment, but they do so in fundamentally different ways. The right choice depends on your property, your budget, and your long-term priorities.

This guide compares both types across every factor that matters, with real UK costs and honest assessments of where each excels.

How Each Type Works

Air Source Heat Pumps (ASHPs)

An air source heat pump sits outside your home and absorbs warmth from the ambient air — even in temperatures as low as -15°C to -25°C. A fan draws air across an evaporator containing refrigerant, which absorbs the heat. This is then compressed to raise its temperature and transferred to your heating system via a heat exchanger.

ASHPs are by far the most common type in the UK, accounting for roughly 85% of all heat pump installations.

Ground Source Heat Pumps (GSHPs)

A ground source heat pump extracts heat from the ground, where the temperature remains relatively stable at 8°C to 12°C year-round (below about 1.5 metres). A loop of pipework buried underground circulates a water-antifreeze mixture that absorbs ground warmth. This is then compressed and transferred to your heating system.

Ground loops come in two main forms:

  • Horizontal trenches: Pipes laid in trenches 1.5 to 2 metres deep, requiring a large area of garden or land
  • Vertical boreholes: Pipes inserted into boreholes drilled 60 to 200 metres deep, requiring less surface area but specialist drilling equipment

Installation Cost Comparison

Air Source Heat Pump Costs

A typical ASHP installation for a three-bedroom house costs between £10,000 and £16,000. This includes:

  • The outdoor unit
  • A hot water cylinder
  • Controls and thermostats
  • Installation labour (typically 2 to 3 days)
  • Any necessary pipework modifications

After the BUS grant of £7,500, the net cost is typically £4,000 to £8,500.

Ground Source Heat Pump Costs

A typical GSHP installation costs between £18,000 and £35,000 for the same property. The higher cost is driven by:

  • The indoor heat pump unit
  • Ground loop installation — horizontal trenches (£3,000 to £8,000) or vertical boreholes (£8,000 to £18,000)
  • A hot water cylinder
  • Groundwork, reinstatement, and landscaping
  • Installation labour (typically 1 to 2 weeks including groundwork)

After the BUS grant of £7,500, the net cost is typically £10,500 to £27,500.

The Cost Gap

Ground source systems cost roughly twice as much as air source systems. The additional expense is almost entirely due to the ground loop — either the excavation for horizontal trenches or the drilling for boreholes. The heat pump units themselves are comparably priced.

Efficiency and Performance

Seasonal Efficiency (SCOP)

Ground source heat pumps are consistently more efficient than air source models:

  • ASHP seasonal COP: 2.8 to 3.5 (typical UK installation)
  • GSHP seasonal COP: 3.5 to 4.5 (typical UK installation)

The reason is simple: the ground maintains a stable temperature year-round, while air temperature fluctuates. In winter — when you need the most heat — air temperatures drop to 0°C to 5°C, reducing ASHP efficiency. The ground stays at 8°C to 12°C regardless of the weather, giving the GSHP a consistent advantage.

What This Means for Running Costs

For a home needing 12,000 kWh of heat annually at 24.50p/kWh electricity:

  • ASHP (SCOP 3.0): Uses 4,000 kWh of electricity = approximately £980/year
  • GSHP (SCOP 4.0): Uses 3,000 kWh of electricity = approximately £735/year

The GSHP saves roughly £245 per year on running costs. Over 20 years (with 3% energy inflation), that adds up to approximately £6,600 in savings.

Does the Higher Efficiency Justify the Higher Cost?

The additional installation cost of a GSHP (roughly £8,000 to £19,000 more than an ASHP) versus the running cost saving (roughly £6,600 over 20 years) means that a ground source system rarely pays for itself through efficiency alone. The economics favour air source for most homes unless the property has specific characteristics that tip the balance.

Land and Space Requirements

Air Source Heat Pump

An ASHP requires:

  • An outdoor unit roughly 1m wide × 0.4m deep × 1m tall (varies by model)
  • A clear space of at least 300mm behind and to the sides, with 3m of unobstructed airflow in front
  • A solid base (concrete pad or ground-mounted bracket)
  • Typically positioned on a side return, back wall, or patio area

Almost any house with a garden, patio, or side passage can accommodate an ASHP. Even many flats with balconies or dedicated external wall space can work.

Ground Source Heat Pump

A GSHP requires either:

  • Horizontal trenches: Roughly 100 to 200 square metres of garden — about the size of a large lawn. The trenches are backfilled after installation, and the garden can be reinstated with grass (but not deep-rooted trees or structures)
  • Vertical boreholes: Much less surface area needed — the drill rig needs access to your garden, and the borehole itself is only 150mm wide. But you need 1 to 3 boreholes drilled 60 to 200 metres deep

GSHPs suit larger properties with gardens, rural homes with land, or new builds where the ground loop can be installed before landscaping.

Noise

Air Source Heat Pumps

ASHPs produce noise from their fan and compressor. Modern units are significantly quieter than older models — typically 40 to 50 dB(A) at 1 metre, comparable to a refrigerator or quiet conversation. Noise levels must comply with permitted development limits, and careful positioning reduces impact on neighbours.

Ground Source Heat Pumps

GSHPs are virtually silent. The heat pump unit sits indoors (or in a plant room), and the ground loop makes no noise whatsoever. If noise is a serious concern — perhaps you have very close neighbours or noise-sensitive family members — a GSHP has a clear advantage.

Lifespan and Reliability

Air Source Heat Pumps

ASHPs typically last 15 to 20 years. The outdoor unit is exposed to weather and contains a fan that will eventually need replacement. Compressor warranties are typically 5 to 10 years.

Ground Source Heat Pumps

GSHPs typically last 20 to 25 years for the indoor unit, and the ground loop itself can last 50 years or more with virtually no maintenance. When the indoor unit eventually needs replacing, you can connect a new heat pump to the existing ground loop at a fraction of the original installation cost.

This long-term durability is one of the strongest arguments for ground source systems in properties where you plan to stay for decades.

Planning Permission

Air Source

Most ASHP installations fall under permitted development rights. The main conditions are:

  • Volume of the outdoor unit must not exceed 0.6 cubic metres
  • Must be at least 1 metre from the property boundary
  • Noise must comply with MCS 020 planning standards
  • Listed buildings and conservation areas may need formal permission

Ground Source

Horizontal ground loops generally do not require planning permission. Vertical boreholes may need an environmental permit from the Environment Agency, particularly if they penetrate aquifers. This adds time and cost to the process.

Which Type Suits Your Home?

Choose Air Source If:

  • You have a standard suburban or urban home with limited garden space
  • Your budget is moderate (especially after the BUS grant)
  • You want the simplest, fastest installation
  • You are replacing a gas or oil boiler and want a straightforward swap
  • Your home is reasonably well insulated

Choose Ground Source If:

  • You have a large garden or land available for ground loops
  • You can afford the higher upfront cost and want maximum long-term efficiency
  • Noise is a critical concern (very close neighbours, sensitive location)
  • You are building a new home and can install the ground loop during construction
  • Your property has a high heat demand and you want the most efficient system possible
  • You plan to live in the property for 20+ years, maximising the ground loop's lifespan advantage

Not sure which type suits you? Use our suitability checker for guidance, or request personalised quotes from MCS-certified installers who can assess your property.

Can You Combine Both?

Hybrid systems that use both an air source heat pump and a ground loop exist but are rare in domestic settings. More common is pairing either type with an existing gas boiler as a hybrid system for the transition period — though this is becoming less necessary as heat pump technology improves.

Frequently Asked Questions

Is a ground source heat pump worth the extra cost?

For most homes, no — the running cost savings do not recover the additional installation expense. However, for large properties with high heat demands, very long-term ownership plans, or new builds where ground loop costs are lower, a GSHP can be excellent value over its lifetime.

Which is more efficient, air source or ground source?

Ground source heat pumps are more efficient, with typical seasonal COPs of 3.5 to 4.5 compared to 2.8 to 3.5 for air source. The ground provides a warmer, more stable heat source than cold winter air.

Do ground source heat pumps work in small gardens?

Vertical boreholes can work in smaller gardens, as they go deep rather than wide. However, the drilling adds significant cost (£8,000 to £18,000) and requires access for a drill rig. For most small gardens, an air source heat pump is more practical.

How long does each type last?

Air source heat pumps typically last 15 to 20 years. Ground source units last 20 to 25 years, and the ground loop itself can last 50+ years, meaning you only replace the indoor unit when the time comes.

Which type qualifies for the BUS grant?

Both types qualify for the Boiler Upgrade Scheme grant of £7,500. The grant amount is the same regardless of whether you choose air source or ground source.

Can I install a ground source heat pump myself?

No. Ground source installations require MCS-certified installers and specialist groundwork contractors. The ground loop design requires engineering calculations based on your soil type, property heat loss, and other technical factors. DIY installation would also disqualify you from the BUS grant.