Ground source heat pumps explained

A ground source heat pump system harnesses natural solar heat stored in 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 for your own home, an air source system is the first choice for most, rather than a ground source heat pump. If you have a large garden, or need cooling, however, a ground source heat pump system might be a better option. 

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

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 fossil fuels. 

Heat pumps are much more environmentally friendly than gas boilers. Heat pumps are zero emissions at the point of use. While you still need to use electricity to power a heat pump (and therefore heat pumps aren't yet zero carbon), our electricity increasingly comes from renewable sources. And, when the grid is completely decarbonised – currently planned for 2035, although the Climate Change Committee says that we are off track from reaching this – all heat pumps would be zero carbon. 

In the meantime, you can improve the carbon efficiency of any heat pump now by generating some of your own electricity with a solar PV system. Or you could pick a more sustainable electricity tariff or company to provide your power. See our guide to green energy suppliers. 

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. 

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 (usually inside your home).

Thermal transfer fluid, a mixture of water and biodegradable anti-freeze, is pumped around the ground loop and absorbs the naturally occurring heat stored in the ground. 

The water mixture passes through a heat exchanger, which extracts the heat to boil the refrigerant in the heat pump. The gaseous refrigerant is compressed which makes it hot. The temperature achieved is controllable. The heat is then transferred to your home heating system and hot water cylinder in a second heat exchanger. 

1. The ground source heat pump uses fluid to absorb heat from the ground.
2. Using electricity, the gaseous refrigerant is compressed and raised to a higher temperature.
3. Heat is transferred to radiators or underfloor heating, or is stored in a hot water cylinder. 
4. Stored hot water can then be used for showers, baths and taps, exactly as with a boiler system. 

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 new-build 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 is an older property with lower levels of 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 also be more expensive. Bigger properties may need more 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 ground source heat pump unit. This may contain an integral hot water cylinder or the cylinder may be separate.

How warm is ground source heating?

A well set-up heat pump (whether that's ground source or air source) that is running properly will heat your home as well as a well set-up fossil fuel boiler. Many home owners with heat pumps report more comfortable heating, with no fluctuations in temperature. 

A ground source heat pump can increase the temperature from the ground to more than 60°C if needed. However, the higher the temperature required, the more electricity you'll use, so you should ensure that the system runs as efficiently as possible at lower temperatures. The required temperature is determined by the outside air temperature, the levels of insulation and the size of the radiators. 

This hot water can then be used in radiators, for hot water or in an underfloor heating system. A well-insulated home can be brought up to temperature with central heating running at 50°C, but you could need higher flow temperatures in winter. If your home leaks a lot of heat, you should 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. Costs are very project specific, but an average UK three-bed home could incur a cost in the range of £204,000 to £30,000 according to the Heat Pump Federation. Drilling boreholes tends to be more expensive, although this isn't always the case because costs depend upon the geology under your home. You can get financial aid towards the cost of a heat pump via the Boiler Upgrade Scheme (BUS). This makes a significant contribution if you're buying an air source heat pump, but a proportionately lower contribution to the higher cost of a ground source heat pump system. 
• Efficiency – the compressor and ground loop circulation use electricity. But for every unit of electricity used by the pump, you get between three and four units of heat, making this an efficient way to heat a building.
• Running costs – cheaper time-of-use electricity tariffs can be used to lower the cost of electricity to power the heat pump. See ground source heat pump costs and savings for more.
• Disruption - the groundworks required to dig the trench can be expensive and disruptive, although most domestic ground source heat pump installations benefit from Permitted Development Rights. Ground source heat pumps can also be a very attractive option in larger and older or listed homes because finances tend to improve with scale. 
• Requirements – all heat pumps are similar to condensing gas boilers in that they benefit from operating at flow temperatures below 55°C. However, new generation heat pumps can provide efficient solutions at higher temperatures if needed in winter. 
• Hot water – heat pumps can provide an efficient solution for hot water, but a cylinder is usually required. That can be a space challenge if you're switching from a combi boiler and are short of indoor space. 

Are ground source heat pumps efficient?

A ground source heat pump system will 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 most carbon when used to replace an old electric heating system (with storage heaters) or an oil-fired 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 tend to be more efficient than air source heat pumps. A typical air source heat pump should be around 280-380% efficient, and a typical ground source heat pump should be 320-420% efficient. But only your installer can give you a reliable estimate tailored to your property. 

Ground source heat pumps extract heat from sub-surface soil or deeper geology which has a more constant year-round temperature than the air during the UK heating system, 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. 

Find out more about how much a ground source heat pump costs and get an idea of how much it would cost to run.