A ground source heat pump, also known as a ground-to-water heat pump or geothermal heat pump, uses captured heat from the ground outside to heat your central heating system and heat the water in a hot water cylinder feeding to all of your hot taps and showers.

A ground source heat pump is made up of a loop of buried pipework that circulates a mixture of water and antifreeze fluid which flows around the ground loop pipe buried in trenches.

Heat from the ground is absorbed into the fluid (thermal transfer fluid -TTF), which then passes through a heat exchanger into the heat pump. This raises the temperature of the fluid and then transfers that heat to water in your central heating, warming your radiators or the water for your hot taps.

Ground source heat pumps are low-maintenance that can provide cooling in summer as well as heating in winter, but they are more expensive than investing in an air source heat pump.

Are ground source heat pumps a good idea?

Less than half of UK homes are suitable to have a ground source heat pump installed. If your property benefits from garden space, then government offers include financial aid (The Renewable Heat Incentive (RHI) scheme) to help with the expensive upfront cost of installing a ground source heat pump. Having one installed will save overall on your energy bills, helping to recover the upfront costs of the installation. The Energy Savings Trust estimates that a ground source heat pump could save you up to £1,400 a year.

For every unit of electricity used by a heat pump, three to four units of heat are captured and transferred to your home. This means that ground source heat pumps are 300 to 400% efficient in terms of its use of electricity.

They let off 70% less carbon dioxide emissions compared to traditional gas boiler systems. If the electricity used to power the pump is provided by renewable energy, carbon emissions can be reduced to zero.

Heat pump systems are safer than gas-fired or oil-fired boilers as they rely on electricity rather than generating heat by burning fuel.

They have less on-going maintenance as there is no need for an annual check as they don’t pose the risk of a carbon monoxide leak. With less need for maintenance comes a longer life span because the ground heat exchanger element of the heat pump installation has a design life of over 100 years.

How much space do I need to install a ground source heat pump?

Mid-terraced homes and blocks of flats are not suitable for a geothermal heat pump as they need outdoor space around your home to be installed. Unless there is a communal piece of garden and the expense agreed to be shared. The heat pump does not need a large garden, but space close by for the trenches and boreholes to be dug. A ground source heat pump needs more space than an air source heat pump. An average horizontal system needs approximately 700 square metres, whereas a vertical borehole system needs enough outside space for the drilling rig to access the site, but boreholes are only approximately 20 centimetres wide.

Installing the ground loop will need earth that is suitable for digging and able to have the necessary machinery to access. The space must be clear from trees because roots will be an issue when creating the trenches. The length of the ground loop and trenches depend on the size of your home and the amount of heat you need.

For a small garden space, boreholes can be drilled vertical to gather the heat. Although, this can be more costly than digging trenches as drilling down will need a specialist ground survey. Larger houses may need multiple boreholes, which must be placed 5-6 metres apart. Borehole depth depends on the heat demand of a property and the underlying geology but is likely to be around 75-200 metres deep.

Inside the home will need space for the indoor heat pump unit, which contains key components. The inside unit will also house the hot water cylinder.

How much will it cost to install a ground source heat pump?

Installing a ground source heat pump is a very costly upfront expense. This can range between £13,000 and £45,000 depending on the type and size of the system. The time installing the heat pump can take up to a week's worth of labour and you may need a landscaper as well as a gas engineer. The installation is dependent on the layout of your garden and access to the ground. If you have the space, trenches will be cheaper than a borehole to lay the ground loop. 

Trenches only need to be dug up to two metres deep, keeping costs anywhere from £13,000- £35,000.

A borehole has to be dug up to a hundred metres deep, resulting in an expense of £30,000 - £45,000.

The brand, model and size of the geothermal heat pump will greatly affect the overall cost as well as the size of the house as this depends on how much heat will be needed from the unit. A new build will be easier to fit a ground source heat pump as there is not yet an established garden and during the building work phase, it should be easier to get the digger into the garden to prepare trenches or boreholes.

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Installing a ground source heat pump system involves work on the outside of the house and the inside;

Outside house preparation

• hiring a digger machine
• hiring a person to control the digger
• digging the trenches
• laying the coils of pipework
  (If not enough space for trenches then two or three vertical boreholes to be dug)

Inside house preparation

• installing the heat pump
• this may include a hot water cylinder
  or may be a small pump fitted in a kitchen cupboard

Heat pumps are also generally installed close to an external wall to give easy access to the ground array pipes but with an electrical power output to run the pump.

How long do ground source heat pumps last?

Ground source heat pumps are long lasting. People can generally get 20-25 years lifespan out of a unit with some lasting as long as 50 years. The pumps are designed well and there is not much that can go wrong with the pump. Of course, longevity will vary depending on model and manufacturer.

Gas boilers tend to need replacing every 12 years or so. So the fact that the heat pump can double that lifespan, coupled with the RHI scheme, makes embarking on such a costly expense more worthwhile.

Usually, the component to break first is the compressor. This is a part that is constantly in use so it tends to burn out and can be replaced without needing to replace the entire ground source heat pump.

Common issues with a ground source heat pump

Before calling out a professional gas engineer, some troubleshooting to do first to diagnose the issue, would be to check that;

• power is communicating to the unit and no tripped circuit breakers
• air filters and coils are clean or replaced if dirty
• the loop pumps are running
• the thermostat is at an appropriate temperature
• heat pump is correctly set to heating or cooling
• there are no signs of leaks or broken wiring 
• water is properly circulating through the heat exchanger
• the pressure inside of the loop system is correct

Common issues with ground source heat pump include;

A decrease in heating or cooling levels
This might be caused by restricted air flow, especially if the air filters appear dirty, replace them to solve the issue.

Cooling function not working
Perhaps a low refrigerant charge which could be caused by the heat exchanger clogged with limescale or a faulty reversing valve. Possible fix might be as simple as repositioning the thermostat for a better and more accurate reading. 

High amounts of indoor humidity
Too much airflow or a unit that is too big for your home. Adjusting the fan motor speed may fix this problem.

Air Temperature too cool
Perhaps from too much airflow and the fan speed needs adjusting.

Estimates for common heating engineer jobs;

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