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Ground source heat pumps explained

How ground source heat pumps work, and their pros and cons
Christina WoodgerSenior researcher & writer
Karen LawrenceSenior researcher & writer
Hot water being run 451052

A ground source heat pump system harnesses natural heat from the ground. 

A heat pump can heat your home efficiently, and reduce your carbon emissions. It can also heat water stored in a hot water cylinder. 

If you're thinking of buying a heat pump, it will likely be an air source, rather than ground source heat pump. If you have a large garden, however, a ground source heat pump might be a good choice. 

A ground source heat pump performs the same role as a boiler in a central heating system. But it uses ambient heat from the ground to generate heat, instead of needing to burn fuel. 

While you still need to use electricity to power a heat pump (and therefore heat pumps aren't zero carbon) our electricity increasingly comes from renewable sources. Therefore heat pumps are much more environmentally-friendly than gas boilers. 

Read on to find out more about how a ground source heat pump works and whether one would be right for your home and budget. 

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

How ground source heat pumps work

Ground source heat pump systems are made up of a ground loop, which is a network of water pipes buried underground, and a heat pump situated at ground level.

A mixture of water and anti-freeze is pumped around the ground loop and absorbs the naturally occurring heat stored in the ground. 

The water mixture gets compressed and goes through a heat exchanger, which extracts the heat and transfers it to the heat pump. The heat is then transferred to your home heating system.

  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 sent to radiators or underfloor heating - the remainder is stored in a hot water cylinder.
  4. Stored hot water can then be used for showers, baths and taps.

How much garden space do I need for a ground source heat pump?

How big the ground loop needs to be depends on how big your home is and how much heat you require, but you'll need plenty of garden space either way. The Energy Savings Trust says, for a newbuild three-bedroom house, you could expect two trenches of 30-40 metres in length, but more space would be needed if your home is larger or an older property with poor insulation. 

The ground loop area will need to avoid trees, as roots will cause problems when digging trenches.

Your garden will also need to be accessible for digging machinery entering from the road. 

If you have less space, it may be possible to drill vertical boreholes to gather heat. This method can be more efficient (as the ground gets warmer the deeper you dig) but will also be more expensive. Bigger properties may need multiple boreholes. 

If your garden is too small for a ground source heat pump, you could install an air-source heat pump instead. These are usually placed outside at the side or back of a property, and take heat from the air.  For more details, see our guide to Air source heat pumps explained.

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

How warm is ground source heating?

A well set-up heat pump (ground source or air source) that is running properly shouldn't leave your home cold. 

A ground source heat pump can increase the temperature from the ground to around 50°C. The hotter you heat your water, the more electricity you'll use.

You can then use this heat in a radiator, for hot water, or in an underfloor heating system. Whether you'll need an additional back-up heating system is dependent on your property. A well-insulated home can be adequately brought up to temperature with central heating running at 50°C, but you might find this insufficient if your home leaks a lot of heat. If your home is poorly insulated, it's advisable to improve your insulation regardless of whether you have a heat pump or a boiler, as you'll be paying to generate energy that is leaking back out. 

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 hugely expensive. It typically costs around £24,000 if your ground loop is buried in trenches, but it can cost as much as £49,000 if you need to dig a borehole (and not including the cost of fitting underfloor heating, if required), according to Energy Saving Trust. You can get financial aid towards the cost of a heat pump via the Boiler Upgrade Scheme (BUS). This makes a huge difference if you're buying an air source heat pump, but it won't cover the full cost of a ground source heat pump. 
  • Efficiency – you need to use electricity to power the pump that circulates the liquid in the ground loop. But for every unit of electricity used by the pump, you get between two and four units of heat – making this an efficient way to heat a building.
  • Running costs – cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump. More on: ground source heat pump costs and savings
  • The groundworks required to dig the trench can be expensive and disruptive – planning permission may be required if space is at a premium and you need a borehole. Ground source heat pumps tend to be better suited to new-build homes, as they can be planned as part of the construction process.
  • Requirements – they are generally not suitable for properties with existing gas-fired central heating. The technology works at lower temperatures, making it better suited to homes with underfloor heating or very large radiators
  • Hot water – If you’re also using the heat pump to provide hot water, it can limit the overall efficiency of the pump. 

Are ground source heat pumps efficient?

A ground source heat pump system can 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 you most carbon when used to replace an old electric heating system (with storage heaters) or coal 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 do typically have better efficiencies than air source heat pumps. While we expect a typical air source heat pump to be around 250% - 300% efficient, we would expect a typical ground source heat pump to be 350% - 400% efficient. But only your installer can give you a reliable estimate that's fit for your property. 

Ground source heat pumps extract heat from soil which has a more constant temperature than the air, 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.