Ground source heat pumps explained How ground source heat pumps work
A ground source heat pump system harnesses natural heat from underground by pumping water through it. The heat pump then increases the temperature, and the heat is used to provide home heating or hot water.
The 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 does in a central heating system, but it uses ambient heat from the ground rather than burning fuel to generate heat. Unlike an air source heat pump, which takes heat from the air.
Read on to find out how a ground source heat pump works, and to find out 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 installation of the system, generally with a garden that's accessible for digging machinery.
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 pump itself consists of an evaporator, a compressor and a condenser - together these take the heat from the water mixture, transfers it to your domestic heating system and increases the temperature in the process. A ground source heat pump increases the temperature from the ground by between one and a half and four times – so if the ground temperature is 12°C, the output would be between 18 and 48°C).
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. See our separate guide to air source heat pumps for more details.
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 home.
Pros of ground source heat pumps
- Ground source heat pumps generate less CO2 than conventional heating systems.
- The Energy Saving Trust (EST) says that a 'typical' ground source heat pump could save you between £410 and £2,000 a year depending which existing heating system you are replacing.
- 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 £2,610 and £3,940 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, and special heat pump tariffs may be available from some electricity suppliers – alternatively consider solar photovoltaic panels or a wind turbine (if you live in a suitable area) for a greener source of electricity.
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 £11,000-£15,000, depending on the size of the system (not including the cost of fitting underfloor heating, if required).
- Ground source heat pumps are generally not suitable for properties with existing gas-fired central heating as the technology works at lower temperatures, making it better suited to homes with underfloor heating. You may need a separate electric heater to help provide all your heating and hot water needs.
- 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.
- You still need to use electricity to drive the pump, so a ground source heat pump can’t be considered completely zero-carbon unless this is provided by a renewable source, such as solar power or a wind turbine. To save further make sure you are on the best electricity tariff.
- 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.
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 EST, a heat pump with mid-range efficiency uses a third of the energy needed in an average gas or oil boiler to produce the same amount of heat.
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.