What Are Ground Source Heat Pumps and How Do They Work?

What Is a Ground Source Heat Pump?

All heat pumps transfer heat from one source to another. They are so efficient that they can amplify any natural heat using electricity in order to heat up your home. A ground source heat pump uses natural heat from the ground to do this and can either supply heat to your radiators or underfloor heating. You can also power your hot water supply using this type of heat pump.

How Do Ground Source Heat Pumps Work?

Ground types work by pumping a special mix of fluid through a series of underground pipes buried in your garden. This is usually in lanes, providing there is room, but can be in boreholes, which are vertical instead of horizontal. These pipes absorb the naturally occurring heat from the ground and warm up the fluid, which is then transferred to a heat exchanger in the ground source heat pump. This amplifies the heat to the point where it can warm your heating and hot water.

They use electricity to operate, but the energy required is much lower than the heat it can output. A ground source heat pump is so efficient that it can generally produce four times as much heat than the electricity required to power it. In colder weather, a heat pump has to work harder to maintain its set temperature, which requires more electricity. Ground pumps are typically more efficient than their air source relatives because the ground is usually between 5 and 15°C throughout the year, which provides more than enough residual heat for them to operate.

What To Consider With a Ground Source Heat Pump

The main issue with heat pumps is that you need the space to lay the external pipework. The longer the pipework, the more heat you’ll be able to generate. If you have a large home with a big heating capacity, you’ll need more room to cover your requirements. Pipework for a ground source heat pump is usually dug 1.5 metres below the ground’s surface in trenches up and down your garden. This depth prevents them from being affected by frost.

If you don’t have space outside, you may need to have boreholes installed instead, but this is a much more expensive method for installation. These are vertically drilled holes that go between 75 and 200 metres deep. Depending on your heating requirements, you may even need more than one.

Heat pumps work to lower temperatures (typically 35-45°C) than fossil fuel boilers (around 75°C), so your ground source heat pump system will most likely take longer to heat up than what you’re accustomed to. For more differences between heat pumps and boilers, see our guide. As such, you will probably need to operate your heating system for longer in order to achieve desired temperatures. This won’t affect underfloor heating as much because it isn’t meant to be operated any higher than 45°C. Also, if you don’t have enough room for the pipes, you may even need a separate electric heater for your hot water supply.

While there are no emissions produced by a heat pump itself, the only emissions associated with it is from how the electricity supplying it is generated. Green electricity suppliers or relying on your own solar panels is the way of getting around this.

Heat pump warranties last for around 10 years, but regular maintenance can ensure it lasts for at least 20 years. Visual inspections are one way you can prolong the life of your heat pump. The fluid in the external pipes should be repressurised by a professional every couple of years to maintain its efficiency.

How Much Do Ground Source Heat Pumps Cost?

According to Energy Saving Trust, a ground source heat pump can cost anywhere between £24,000 and £50,000, but this depends on a number of factors. These include:

• Trench or borehole system

• Model (e.g., Vaillant heat pumps)

• Heating requirements

• Size of property

• Replacement heating system (bigger radiators or underfloor heating)

If you are having a bigger ground source heat pump system installed, this will be more invasive and will require additional costs. Your existing heating system may also need to be updated to compensate for the lower pressures heat pumps work to. Greater surface areas are needed, so either larger radiators should be fitted or underfloor heating instead. This will affect your total bill.

With ground source heat pumps, you’re also able to make use of the discount from the Boiler Upgrade Scheme. This entitles you to £7,500 off its installation. Your installer will let you know if you qualify and will sort out the forms for you. It will work out as a discount off your total bill.

According to data from MCS, the average cost of these heat pumps in 2022 was £19,813. You can see how the price fluctuated throughout the year in the graph below.

Ground Source Heat Pump Running Costs

This depends on the climate and how efficiently your system is running. Colder weather and a higher heating requirement will increase the amount of electricity that is needed, which will cost you more in bills. A ground source heat pump has the potential to reduce your yearly energy bills by up to £2,500 a year. This can save between 2,300 and 11,000kg of CO₂ equivalent a year, depending on your existing heating system.

If you have your own solar array, you can offset any electricity to reduce these costs even further. It’s not impossible to run your heat pump exclusively on solar power, but it would depend on the size of your solar panels and your heating requirements. A smaller home would be theoretically easier to run on a solar powered ground source heat pump.

Ground Source Heat Pump Efficiency

The efficiency of a ground heat pump depends on the outside temperature. Fortunately, the ground is more efficient than the air as it always holds more heat during the year. The colder it is, the more electricity your heat pump needs to generate the same amount of heat.

Heat pumps need larger surface areas for heating to account for their lower water pressure. This means that the greater the amount of heat, the bigger the surface required. Bigger radiators are needed, but underfloor heating is best suited to a ground source heat pump. Alternatively, you can run your heating system for longer, but this will cost you in efficiency. A well designed system uses less electricity, which is cheaper to operate.

The Coefficient of Performance (CoP) and Seasonal Coefficient of Performance (SCoP) are measures of efficiency in ground source heat pumps that give an indication of running costs and total efficiencies. The SCoP is considered the more accurate of the two as it gives a measure across the whole year. These are useful indicators when looking for a heat pump and can tell you from the offset if you’ll be saving money.

Insulation Needed for a Ground Source Heat Pump

The final point about heat pumps is that they only work with a home that is properly insulated in the first place. Good insulation helps reduce operating costs as it’s better at heat retention and stops your heat pump from working as hard to maintain its set temperature. If your home isn’t yet ready for a ground source heat pump, it needs to be sufficiently insulated first.

Pros and Cons

We’ve included the benefits and drawbacks to installing a ground source heat pump in the table below for a quick summary.