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.
They need electricity to run, but the idea is that they use less electrical energy than the heat they produce.
The 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 more on how a ground source heat pump works, and to see whether it's right for your home.
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.
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 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.
You'll need plenty of 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.
A ground source heat pump can increase the temperature from the ground to around 50°C, although the hotter you heat your water, the more electricity you'll use.
Ground source heat pumps generate less CO2 than conventional heating systems, but you still need to use electricity to drive the pump. That means they can’t be considered completely zero-carbon unless the electricity is provided by a renewable source.
The Energy Saving Trust (EST) says an 'average' ground source heat pump could save you up to £1,400 a year, or could add up to £65 to your annual heating bill, depending which heating system you're replacing.
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.