Ground source heat pumps explained

Ground source heat pumps (GSHPs) harness heat stored underground to provide your home with space heating and hot water.

They work in the same way as air source heat pumps, but they draw warmth from the ground rather than from the air.

Heat pumps are more environmentally friendly than gas or oil boilers as they produce no carbon emissions at the point of use. While you still need electricity to run them, UK grid electricity increasingly comes from renewable sources, so it causes much less environmental harm than fossil fuels such as oil, gas and LPG. 

Read on to find out more about how much space you need for a ground source heat pump, the likely costs and savings, whether it is the right choice for your home. 

Heat pumps vs boilers: the key things you need to know

Should you buy a ground source heat pump?

Here are five key things you need to think about if you are considering installing a ground source heat pump:

1. The size of your home and garden

Ground source heat pumps are better for larger homes that use a lot of heat. You'll need enough outdoor space to install the ground array, including access for specialist digging machinery. Ask an installer to assess whether your home and garden are suitable.

2. Existing fuel and heating system

Energy bill savings will be greater if you're replacing an old or expensive heating system (such as LPG or direct electric heating) than if you're currently using mains gas. If you don't already have a wet central heating system - that is, one with radiators and/or underfloor heating fed by hot water pipes - you'll have to install the entire system from scratch, which will increase the upfront cost and be more disruptive.

3. Existing radiators

A ground source heat pump produces low-temperature heat, so is best connected to a system that's designed for this, such as underfloor heating.

If your existing radiators are small and you're used to having them scorching hot, they may not be able to heat your home as quickly or as effectively. You may need to add more radiators, or replace them with larger radiators and/or underfloor heating, all of which will increase the total installation cost.

4. Water heating

If you are replacing a combi boiler and don't have a hot water tank, you'll need a suitable space to install a new hot water storage cylinder. Alternatively, if you install a heat-only heat pump, you'll need a separate method of water heating, such as an immersion heater.

5. Insulation

Before installing a ground source heat pump, check your home's energy efficiency. If appropriate, add loft and cavity wall insulation, or other energy-saving measures to ensure your heat pump runs as efficiently as possible.

If your home is not well insulated, you'll be paying more to generate heat that quickly leaks out of your home.

Find out more about how to insulate your home.

How ground source heat pumps work

Ground source, or ground-to-water, heat pumps use pipes containing thermal transfer fluid - a mixture of water and biodegradable anti-freeze, also known as the 'brine' - to absorb the naturally occurring thermal energy stored in the ground. 

The pipes may be laid either as a series of coils or 'slinkies' in shallow trenches, or as a vertical loop in a deep borehole. The type you choose will largely depend on how much land you have and the local geology.

The warmed brine circulates back to the heat pump, where a compressor increases its temperature. A heat exchanger then transfers the heat to radiators, underfloor heating and storage cylinders to provide heating and hot water. 

After the heat has been delivered to your home, the brine passes through an expansion valve before circulating through the ground loop once again to absorb more heat.

1. The ground source heat pump uses fluid to absorb heat from the ground.
2. Using electricity, the fluid is compressed and raised to a higher temperature.
3. Heat is transferred to water that can then be piped to radiators or underfloor heating, or stored in a hot water cylinder. 
4. Stored hot water can also be used for showers, baths and taps.

Just like air-to-water heat pumps, a ground source heat pump can directly replace an existing gas or oil boiler, connecting to your existing heating system; however, you may need a new hot water cylinder, pipework, and larger radiators.

How much land do you need for a ground source heat pump?

If you're considering switching to a heat pump, an air source heat pump is a more suitable choice for most homes because they are cheaper to buy and install and don't require much space.

However, ground source heat pumps are more efficient, especially during the winter months. They extract heat from sub-surface soil or deeper geology which has a more constant year-round temperature than the air during the UK heating season, and rarely goes below 5°C, so it is remains efficient during cold weather. An air source heat pump may be very efficient on a mild day and more expensive to run during a cold snap. 

If you live in one of the colder parts of the country, have a large property and/or high heating demand, and have sufficient land, you might consider a ground source heat pump.

The size of the ground loop will depend on the size of your home and how much heat you need. You may need more space if your home is larger or is an older property with lower levels of insulation.  

Your garden, or other area of land, must be accessible for digging machinery, and the ground loop area must be clear of tree roots.

If you have a smaller garden area, it may be possible to drill vertical boreholes instead. The borehole is only about 20cm wide, but somewhere between 75 and 200 metres deep. The depth depends on the heat demand of your home and the underlying geology. This method can be more efficient in operation (as the ground gets warmer the deeper you dig), but they are more expensive to install. Bigger properties may need more than one borehole. 

Horizontal and vertical arrays: what's the difference?

The ground array (the network of pipes pumping the thermal transfer fluid underground) can be laid horizontally or vertically. The type of system you choose depends on the space you have available and the local geology.

Horizontal systems use lengths of pipe laid in shallow trenches around one to two metres deep.  As a rule of thumb, you'll need 10m of trench with per kilowatt of the heat pump size. So, a 4kW heat pump will require 40m of trench with pipes buried in the ground for space heating. If you need it to supply hot water as well, the trench will need to be slightly longer.

The Ground Source Heat Pump Association estimates that a new-build three-bedroom house (around 120m²) would need two trenches of 30 to 40 metres long.

Horizontal ground arrays require more ground area than vertical arrays like boreholes, but they are cheaper to install because there is no need for specialist drilling equipment.

Vertical arrays bury the pipes in a deep borehole. Depending on the size of the system, the borehole could be up to 200 metres deep, although it is less than a metre in diameter.  

The heat pump unit (containing the compressor and heat exchanger) will be installed inside your home. You'll generally need a space approximately the size of a fridge-freezer, although smaller versions - around the size of an under-counter fridge - are available for smaller homes.

You'll also need a large hot water cylinder - a similar size to the heat pump unit - and possibly a smaller buffer or header tank as well.

Ideally you'll have a plant room or utility room to contain all the components, along with the associated pipework and controls.

Whatever type of ground source heat pump you install, it's important that the system is correctly sized for your heating needs.

If your garden is too small for a ground source heat pump, head to our guide to air source heat pumps.

How much does a ground source heat pump cost?

The cost of a GSHP is closely related to its capacity - the amount of heat it can deliver - so generally,  the greater your heat demand, the larger the heat pump and the higher the installation cost.

The government's Boiler Upgrade Scheme (BUS) offers grants to support the installation of heat pumps.

The latest statistics show that the cost of ground source heat pump installation for homeowners receiving a grant ranged from around £18,000 to £42,000, with the average (median) being around £27,000. That is for installations in England and Wales between April and June 2026 and does not include the grant payment, so the price paid by homeowners would be up to £7,500 less (or up to £9,000 less for off-grid homes currently heated by oil or LPG).

Financial help is available via the Boiler Upgrade Scheme in England and Wales, or the Home Energy Scotland Grant and Loan. 

Find out more about the Boiler Upgrade Scheme and how to apply.

How to calculate ground source heat pump savings 

To get a better idea of how much a ground source heat pump would cost to run, and whether it would be cheaper than your existing heating system, you can make a rough calculation using your own data.

We've worked out an example, below, for a typical household currently using a gas boiler.

Existing heating and hot water costs using gas

Typical household gas consumption is 9,500kWh a year, according to Ofgem's Typical Domestic Consumption Values (TDCV) calculations for a 'medium' consumption household. Your own consumption may be higher or lower than that. 

Gas used for cooking makes up around 2.5% of the total (237.5kWh), so that leaves 9,262.5kWh a year as the typical quantity of gas used for heating and hot water in your home.

From October 2026, the average rate for gas for price capped direct debit customers is 7.97p per kWh (£0.0797 per kWh). The annual cost of typical gas consumption is 9,262.5 x £0.0797 = £738.22 (rounded to £738).

From October 2026, the average gas standing charge is 29.68p per day (£0.2968 per day) so the annual standing charge cost is 365 (days) x £0.2968 = £108.33 (rounded to £108). That makes the total gas bill for heating and hot water (excluding cooking) approx. £846.

What's your heat demand?

To calculate the cost of running a heat pump, you need to work out your household heat demand using your current annual gas consumption and boiler efficiency.

A new A-rated gas boiler must be a minimum of 92% efficient; however, studies have shown that the actual in-use performance is generally lower. Older boilers are also less efficient, so we've assumed an average of 85% efficiency.

As calculated above, energy consumption for heating/hot water is 9,262.5kWh but, as only 85% of gas is being turned into heat, we calculate actual heat demand at 9,262.5 x 0.85 = 7,873kWh.

Potential heating and hot water costs using a heat pump

A typical ground source heat pump can generate 3.5 to 4.5 units of heat for each unit of electricity it uses. We've assumed a COP (Coefficient of Performance) of 4.0 (i.e. 400% efficient) for the following example. To deliver the heat demand of 7,873kWh, the amount of electricity required will be 7,873 ÷ 4 = 1,968.25kWh.

From October 2026, the price cap for electricity is 26.32p per kWh, or £0.2632 per kWh. So the annual cost of electricity for heating and hot water is 1,968.25 x £0.2632 = £518.04 (rounded to £518).

We've assumed that all households already pay the standing charge for electricity, so there's no need to add this. It is an average 54.83p a day, or £200 a year.

Which is cheaper – gas boiler or ground source heat pump?

In this example, the ground source heat pump is cheaper to run, saving £328 a year on average. If your gas boiler is less efficient, or you install a more efficient heat pump, then you will see greater cost savings by switching to a heat pump.

Changes in energy prices will affect future comparisons. If the unit price of gas rises more quickly than the unit price of electricity, then the cost benefit of a heat pump will be greater.

What other costs are involved in buying a ground source heat pump?

If you plan to replace your gas boiler with a ground source heat pump, you may also consider swapping your gas cooker for an electric one. Retaining a gas supply just for cooking will mean the standing charge is disproportionately high. 

If you terminate your gas supply, you may have to pay for removal of the meter. The cost varies according to supplier. If you don't remove the meter, you must continue to pay a standing charge.

Can I install a DIY ground source heat pump?

Installing a ground source heat pump is not a DIY job. Although you may be able to carry out some of the work yourself - such as digging the trenches for a ground loop - the sizing, design and installation should be done by a suitably qualified professional.

If you're ready to find out more, look for a Microgeneration Certification Scheme (MCS) certified installer. Using an MCS certified installer ensures that the equipment meets good standards of performance and that installers are technically safe and competent.

Only MCS installers can apply for the Boiler Upgrade Scheme grant on your behalf.

The MCS website also lists MCS-certified products, including ground source and air source heat pumps, that comply with specific standards for quality, reliability and performance.

Use our Which? Trusted Traders search tool below to find an accredited trader near you. All of our traders have been vetted so you can trust them to do a great job and all are MCS certified.

Do you need planning permission for a ground source heat pump?

The installation of a ground source heat pump is usually considered permitted development, so you don’t need planning permission. As ever, if you live in a listed building or a conservation area you should contact your council to check on local requirements.

Because the heat pump unit can be installed indoors, there is normally no visual change to the exterior of your home. Ground source heat pumps operate quietly and, as the unit is inside your home, there is no noise impact on neighbouring properties.