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6 January 2021

How ground source heat pumps work

We explain how ground source heat pumps work, so you can decide whether one may be right for you.
Hot water being run 451052
Which? Team

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.

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 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.

How they work

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.

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.

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 will depend on your property.

Alternatively, you could try an air source heat pump. 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 and cons

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.

The Renewable Heat Incentive (RHI) scheme provides payments to householders who have a heat pump, estimated to be between £2,335 and £2,750 a year for an average four-bedroom detached home.

Pros Cons
Financial aid – you can get financial help towards the cost of a ground source heat pump. Expensive installation – 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.
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. Disruptive construction – 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.
Cut costs – cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump. 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.

It's also worth noting that you may need a separate electric heater to help meet 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. Ground source heat pumps tend to be better suited to new-build homes, as they can be planned as part of the construction process.

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.

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.

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