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 perform the same role as a gas, oil or LPG boiler in a central heating system, but use ambient heat from the ground instead of burning fossil fuels.

Heat pumps are more environmentally friendly than gas boilers as they produce no carbon emissions at the point of use. 

While you still need electricity to power a heat pump, UK grid electricity increasingly comes from renewable sources. When the grid is completely decarbonised – currently planned for 2035 – all electric heating, including heat pumps, will be zero carbon. 

Read on to find out more about how a ground source heat pump works and whether it is the right choice for your home. 

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How ground source heat pumps work

Ground source 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.

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 the most obvious 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. 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 be in a position to 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, but you'll need plenty of space in any case. The Energy Saving Trust estimates that, for a new-build three-bedroom house, you'll need two trenches of 30-40 metres in length. 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. 

Inside your home you will need space for the indoor heat pump unit. This may contain an integral hot water cylinder or the cylinder may be separate.

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

How warm is ground source heating?

A well set-up heat pump (whether that's ground source or air source) that is running properly will heat your home as well as any fossil fuel boiler. Many home owners with heat pumps report more comfortable heating, with no fluctuations in temperature. 

A ground source heat pump can increase the temperature from the ground to more than 60°C if needed. However, the higher the temperature required, the more electricity you'll use, so you should ensure that the system runs as efficiently as possible at lower temperatures. The required temperature is determined by the outside air temperature, the levels of insulation and the size of the radiators. 

This hot water can then be used in radiators, for hot water or in an underfloor heating system. A well-insulated home can be brought up to temperature with central heating running at 50°C, but you could need higher flow temperatures in winter. If your home leaks a lot of heat, you should improve your insulation regardless of whether you have a heat pump or a boiler, as you'll be paying to generate energy that is rapidly being lost.

Find out more about insulating your home including what to do and why this matters so much.

What to consider when buying a ground source heat pump

• Installation costs – installing a ground source heat pump can be much more expensive than other types of heating. According to the Heat Pump Federation, a GSHP for an average UK three-bed home could cost in the range of £20,000 to £30,000, which is around twice the cost of an air source heat pump installation. Drilling boreholes tends to be more expensive, although this isn't always the case. You can get a grant towards the cost of a heat pump through the Boiler Upgrade Scheme (BUS) but the maximum benefit (£7,500) is the same whether you choose a ground source or air source heat pump.
• Efficiency – a GSHP is much more efficient than a fossil fuel boiler. For every unit of electricity used by the heat pump, you get between three and four units of heat, making this an efficient way to heat a building.
• Running costs – cheaper time-of-use electricity tariffs can be used to lower the cost of electricity to power the heat pump. See ground source heat pump costs and savings for more.
• Disruption - the groundworks required to dig the trench or borehole can be expensive and disruptive, although most domestic ground source heat pump installations benefit from Permitted Development Rights. Ground source heat pumps can also be a very attractive option in larger and older or listed homes because finances tend to improve with scale. 
• Requirements – all heat pumps are similar to condensing gas boilers in that they benefit from operating at flow temperatures below 55°C. However, new generation heat pumps can provide efficient solutions at higher temperatures if needed in winter. 
• Hot water – heat pumps can provide an efficient solution for hot water, but a storage tank or cylinder is required. That can be a challenge if you're switching from a combi boiler and are short of indoor space. 

Are ground source heat pumps efficient?

A ground source heat pump system will help to lower your carbon footprint as it uses a renewable, natural source of heat – the ground. According to the Energy Saving Trust, a heat pump with mid-range efficiency would save most carbon when used to replace an old electric heating system (with storage heaters) or an oil-fired heating system. 

Whether or not you get a heat pump, visit our energy comparison service to use our ratings and expert advice to help choose the right energy tariff for you.

Are ground source heat pumps more efficient than air source heat pumps?

While much more expensive to install, ground source heat pumps tend to be more efficient than air source heat pumps. A typical air source heat pump should be around 280-380% efficient, and a typical ground source heat pump should be 320-420% efficient. But only your installer can give you a reliable estimate tailored to your property. 

Ground source heat pumps extract heat from sub-surface soil or deeper geology which has a more constant year-round temperature than the air during the UK heating system, and the soil shouldn't go below 5°C in the year.

This also means that a ground source heat pump will have less efficiency variance throughout the year, while an air source heat pump may be very efficient on a mild day and more expensive to run during a cold snap. 

Find out more about how much a ground source heat pump costs and get an idea of how much it would cost to run.