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Ground source heat pumps explained

How ground source heat pumps work

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How ground source heat pumps work

We explain how ground source heat pumps work and their pros and cons, so you can decide whether a ground source heat pump is right for you.

A ground source heat pump system harnesses natural heat from underground by pumping water through it in pipes. The heat pump then increases the temperature, and the heat is used to provide home heating or hot water. 

The ground source heat pump needs electricity to run, but the idea is that it uses less electrical energy than the heat it produces.

The heat pump performs the same role as a boiler in a central heating system. But it uses ambient heat from the ground, rather than burning fuel to generate heat. 

Read on to find out how a ground source heat pump works, and to see whether it's right for your home.

What is a ground source heat pump?

Ground source heat pump systems are made up of a ground loop (a network of water pipes buried underground) and a heat pump at ground level. 

You'll need sufficient space for the system to be installed - generally a garden that's accessible for digging machinery. How big the ground loop needs to be depends on how big your home is and how much heat you need.

How a ground source heat pump works

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 is then 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.

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

This heat can then be used in a radiator, hot water or in an underfloor heating system. Whether you'll need an additional back-up heating system will depend on the individual property.

Air source heat pumps are also available. These are usually placed outside at the side or back of a property, and take heat from the air. For more details, see our separate guide to air source heat pumps.

Pros of ground source heat pumps

  • Ground source heat pumps generate less CO2 than conventional heating systems.
  • The Energy Saving Trust (EST) says a 'typical' ground source heat pump could save you up to £1,200 a year, or add up to £50 to your annual heating bill, depending which heating system you're replacing. You can find out more information on ground source heat pump costs and savings
  • You can get financial help towards the cost of a ground source heat pump. The Renewable Heat Incentive scheme provides payments to householders who have a heat pump, estimated to be between £2,380 and £2,575 a year for an average four-bedroom detached home.
  • You need to use electricity to power the pump which 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.
  • Cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump.

Don't pay more for energy than you need to. Use our independent switching site, Which? Switch, to make sure you're on the cheapest gas and electricity tariff for your home.

Cons of ground source heat pumps

  • Installing a ground source heat pump is expensive – typically £10,000 to £18,000, depending on the size of the system (not including the cost of fitting underfloor heating, if required), according to the EST.
  • Ground source heat pumps 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. 
  • You may need a separate electric heater to help provide all your heating and hot water needs. If you’re also using the heat pump to provide hot water, it can limit the overall efficiency of the pump.
  • 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.
  • Your home may take longer to heat up, and you'll need to have your heat pump on for more hours a day than you would with a boiler.
  • You still need to use electricity to drive the pump. So a ground source heat pump can’t be considered completely zero-carbon unless the electricity is provided by a renewable source. 

Looking for a greener source of electricity? Find out about solar photovoltaic panels or a wind turbine.

How green is a ground source heat pump?

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.

A heat pump also requires a supplementary source of power, usually electricity, to power the heat pump. So there will still be some resulting CO2 emissions.