Ground source heat pumps are well established as a low-carbon heating solution, and a long-term alternative to using fossil fuels to heat your home and hot water. But, unlike other heat sources, there's a heavier amount of work and investment involved upfront that can limit their viability in certain homes.
On a positive note, for those homes that do suit the use of a ground source heat pump, the outcome is an efficient, long-lasting, low-carbon system, with little maintenance requirements.
In this expert guide to ground source heat pumps we'll take a look at how they work, the different types, the pros and cons and what you can expect to pay and get back in return.
Types of ground source heat pump
Ground source heat pumps may seem complex compared to air source heat pumps, but they are quite simple bits of kit. They use a series of buried pipes that extract the energy from the sun that warms the ground. The heat pump then amplifies that energy into useful heat for your home.
There are two ways in which the heat is extracted from the ground. A horizontal array where pipes are laid around 1m below ground over a large surface area. A vertical or borehole array is a loop of pipe that, as the name suggests, goes vertically down into the ground.
In addition there is a water source heat pump, which while slightly different, does normally get considered in the ground source heat pump category – information which is all important to know when asking 'is my home suitable for a heat pump'.
Which one you choose will be dependant on a number of variables. “It really comes down to the space you have outside and what’s practical for your plot," says David Billingsley, sales director at Kensa Heat Pumps.
"If you’ve got plenty of land, a horizontal ground loop is often the best option. If space is tighter, vertical boreholes may be the best solution. A reputable company will assess your garden and access, then recommend the best solution for your home. There’s no one‑size‑fits‑all, which is actually a good thing, as it means it is tailored to your home and needs.”
1. Horizontal ground array
Formed from either straight pipes or coiled pipes (known as slinkies), there is no technical or efficiency difference between the two types of pipe used in ground source heat pump installations, and the installer (together with the manufacturer), will advise which is best for your situation.
Whether you choose a horizontal array often comes down to how much space does a ground source heat pump need.
Both straight and coiled pipes should ideally be 1.2m below ground level, and equally as important as the depth, is the spacing between the pipes. As the horizontal ground array is collecting heat introduced to the ground by the sun, pipes need to be spaced sufficiently far apart to ensure they do not take more heat than they should and chill the ground.
The guidelines are 3m for straight pipes and 5m for slinkies (assuming clay soil but wider for other soil types). In addition, pipes need to be at least 5m from the boundary with any adjoining property.
2. Vertical array
A vertical array will have boreholes drilled into the ground and connected across their tops.
The number and depth of boreholes will be dictated by the size of the heat pump and the geology. These can be anything from 70m to 120m deep.
As the temperature of the ground rises, it is often advantageous to have fewer, deeper boreholes, but that is not always possible. As an example, a 8kW heat pump is likely to need at least three boreholes around 70m deep.
They do not need a large area of land and if the price is right, a vertical array is a good option. However, the price of boreholes can vary hugely across the country.
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3. Water source heat pumps
Though far less common, you can also make use of bodies of water, such as lakes, rivers, ponds and streams, using a ground source heat pump system. Known as water source heat pumps, pipes are installed via pond mats submerged into the water.
Not only does this remove the need for disruptive digging, but the return energy to the heat pump is generally 5-6°C higher than standard collectors, improving the overall efficiency.
Equipment that will need to be located inside your house
In terms of what's inside your house, both types will require a heat pump which can either be in a cupboard, or a dedicated plant room, often located on an outside wall to provide easy access to the pipework. Some units also include a hot water cylinder and this can be the size of a large filing cabinet.
“Inside the house, a ground source heat pump doesn’t take up much space at all," confirms David Billingsley. "The indoor unit often fits neatly into a utility room or plant room. Because everything is indoors, there’s no bulky unit or tank outside, which many homeowners really like.”
David Billingsley is Sales Director for the General Market at Kensa Heat Pumps, where he leads engagement with homeowners and installers across the UK. With over 20 years’ experience in the heating industry, David brings a strong background in technical sales and a deep understanding of renewable heating technologies, particularly ground source heat pumps. At Kensa, David plays a key role in supporting the transition to low‑carbon heating, working closely with customers and industry stakeholders to help make heat pumps a practical, affordable and reliable choice for homes across the country.
How does a ground source heat pump work?
Once the pipes have been installed, a mix of water and anti-freeze is pumped around the ground array pipes to absorb the low-grade heat provided by solar energy and stored in the ground.
The heat pump uses compression and expansion technology (as your fridge does), to extract and amplify that heat, increasing the temperature and making it useful in the house.
The ground loop of any ground source heat pump is made up of a number of pipe loops – anything from 2 loops to 12 loops – that are connected to a manifold in a bespoke chamber in the ground. There are then two slightly larger bore pipes that connect the manifold to the heat pump unit in the house.
The amount of heat that can be collected will be dictated by the soil conditions and the amount of unshaded land available. Clay, for example, holds more heat than sand.
As a rule of thumb, an area of 50m2 is needed for each 1kW of heat output. So an 8kW heat pump will need 400m2, assuming damp clay soil. (For context, a tennis court is 260m2.)
Before installing a ground source heat pump, a good installer will investigate the ground conditions to determine the type of soil, if there is sufficient space for a horizontal array, or if boreholes will be necessary.
Advantages of ground source heat pumps
There a good number of benefits to ground source heat pumps vs gas boilers, says David Billingsley.
“The biggest benefits are efficiency, comfort and reliability. Ground source heat pumps deliver very steady heating all year round, they’re extremely quiet, and they cost less to run than all other alternatives.
They also last a long time – the underground pipework can last over 100 years," he notes. "While other systems may have slightly cheaper upfront costs, GSHPs stand out for their longevity, low running costs and long-term performance. Once installed, they’re very much a fit‑and‑forget solution.”
Other benefits include:
- If you sign-up to a renewable energy-only electricity supplier then CO2 emissions for the whole house, not just the heating system, will be effectively zero.
- They work with other renewables. You could also consider running a ground source heat pump along with solar PV panels to provide electricity for the heat pump
- The Boiler Upgrade Scheme is available to help offset some of the costs of ground source heat pumps
Disadvantages of ground source heat pumps
While the long-term benefits of ground source heat pumps are undeniable, it's the initial investment and disruption that can be off-putting to some homeowners.
The high capital cost of installing a ground source is prohibitive to many, and there will be significant disturbance to the garden, particularly when installing a horizontal ground array.
As with installing an air source heat pump, you may also need to factor in the cost of upgrading your home's insulation and could need to replace some types of radiators for low-flow versions, larger ones or even underfloor heating.
Cost & efficiency of ground source heat pumps
Efficiency is stated as the CoP (coefficient of performance) and a typical figure for a ground source heat pump would be around 4.0.
This means that for each 1kW of electricity used to drive the heat pump, it will produce 4.0kW of heat. It is primarily this efficiency of around 400% that makes ground source heat pumps a good idea.
“Ground source heat pumps are the most efficient heating systems available," confirms David Billingsley. "They typically deliver four units of heat for every unit of electricity used.
"Because they draw heat from the stable temperature underground, they perform consistently all year round – even in very cold weather," he confirms, "which helps keep running costs low and energy use predictable.”
As GSHP’s are electrically operated, the homeowner will also have flexibility to access smart tariffs via their utility provider and further reduce the GSHP’s operating costs.
The key issues to reducing your initial costs and ensuring low running costs and high efficiency are:
- Taking a fabric first approach to your home – as with any form of heating, a well-insulated house helps. It could mean you need a smaller heat pump, a smaller ground array (or fewer boreholes) and require less electricity to power it – reducing both your capital and running costs
- Installing a well-designed system as specifying a heat pump is more complex than specifying a gas boiler. It is common to over-specify the size of your gas boiler ‘just in case’, but this is not a good idea when it comes to heat pumps. An over-sized system is more expensive and operates less efficiently than the right sized one
Costs for ground source heat pumps
Complete ground source heat pump costs for a 240m2 home, including installation, will start from around £16,000 but there are a number of factors which impact the costs including:
- The complexity of the installation, including the distance from the heat pump unit to the ground loop manifold chamber which will add to the installation cost
- The type of installation – more specifically, whether a horizontal or vertical array is required
- Bigger properties will need larger heat pumps, even possibly more than one unit, alongside a more complex hydraulic design
“Ground source heat pumps (GSHP’s) are a bigger upfront investment than traditional heating systems," agrees David Billingsley, but the funding and returns can be considerable.
"Homeowners in England and Wales can currently access up to £7,500 per heat pump through the Boiler Upgrade Scheme, which makes a real difference," he notes, "and when you factor in much lower running costs and a system that can last decades, many people see it as a long‑term investment delivering heating for generations, rather than a bolt-on short-term fix.”
FAQs
What size ground source heat pump will I need?
Big enough to heat the house, and no more is the general advice. A modern 4-bedroom house is likely to need an 8kW heat source but could often have a 20kW boiler installed.
There are commercial and technical reasons for this oversizing a gas boiler, but a heat pump is not the same. In that situation the heat pump would need to be 8kW and no more, to achieve maximum efficiency.
A good installer will calculate the exact amount of heat needed for the house to determine the size of the heat pump needed.
Do I need planning permission for a ground source heat pump?
There is nothing externally visible, and a ground source heat pump is usually considered as a Permitted Development so you shouldn't require planning permission. However, if the property is in a conservation area or overlooked by a listed property, it is wise to consult your local authority first.
What are hybrid ground source heat pumps?
Hybrid heat pumps are, in essence, one system that contains both a heat pump and a boiler. The benefits of these systems are that the right heating system can be used to suit the right temperature, helping to reduce running costs, while also keeping carbon emissions as low as possible.
Due to the low-temperature nature of ground source heat pumps, they're better suited to heating a well-insulated home at a milder temperature, while when the temperature drops very low outside, the requirements of the GSHP to reach the heating levels required inside makes it less efficient.
In a hybrid heat pump, at this point a boiler would kick in, ensuring that gas (and potentially other fuels such as hydrogen in the future) are used when it becomes the more efficient option.
Can I install a ground source heat pump myself?
No, it's not advisable to install a ground source heat pump yourself as a DIY project. Installing both the heat pump and the ground array are technically complex tasks, best left to trained, experienced installers.
“Ground source heat pumps need to be designed and installed by trained professionals – particularly the groundworks and electrical connections – so it’s not a DIY job in the traditional sense," says David Billingsley.
What's more, to qualify for Boiler Upgrade Scheme, the system must be installed by an MCS-accredited supplier.
"However, homeowners often get involved early on by planning layouts, timing installations with building work, or coordinating ground array trenches or landscaping if they have a self‑build or renovation project,” notes David.
Those well-versed in groundworks, or using a digger and dumper, may also wish to dig the ground trenches for a horizontal array themselves. Digging boreholes for vertical arrays requires specialist equipment and should always be left to the professionals.
How do I find a good ground source heat pump installer?
The key to installing a ground source heat pump is finding a trustworthy installer who will design and size your system and a good starting point is to choose a member of the GSHP Association and/or use a MCS registered installer.
The indicators of a good installer would be someone who checks the soil conditions and offers quality equipment. But it also usually comes down to due diligence: checking the installer’s history and the references they supply.
Can you use a ground source heat pump with radiators?
The short answer is yes. Ideally, these need to be low-flow radiators, sized and designed to work with heat pumps. They are typically larger than standard radiators.
This is because standard radiators are designed to work with the high flow temperature available from a gas or oil boiler. However, increasing the surface size of standard radiators can also help ensure enough heat is available.
What maintenance does a ground source heat pump need?
Heat pumps are not maintenance free, and it's important to know how to maintain a heat pump properly, but as they are sealed systems the maintenance burden is fairly low. Like any heating system they need an annual check of the main components.
Are ground source heat pumps noisy?
One of the more common heat pump myths – all heating products make some noise, but heat pumps are usually quieter than fossil fuel boilers. The loudest ground source heat pumps may reach 42 decibels, whereas a modern boiler will be around 40-60 decibels.
Can ground source heat pumps provide cooling?
It may also come as a surprise that ground source heat pumps could also be a cooling solution for your home.
Kensa Heat Pumps technical director, Dan Roberts, explains: “Heat pumps are pivotal to heat decarbonisation, but very few are aware of their cooling capabilities. Along with being a highly efficient heating source ground source heat pumps can also provide environmentally friendly, extremely low-cost cooling and overheating protection.
“Kensa’s ground source heat pumps can be set up to deliver ‘passive cooling’, where the system uses the low ground temperature to provide cooling for a building," says Dan.
"Within this system, it’s not necessary to power a compressor and it only takes a small circulation pump and fan to distribute the cool air to the property effectively, preventing overheating for a fraction of the cost of what's required to run traditional air conditioning."
While the cost of a ground source heat pump is more than installing or replacing a gas boiler, it’s worth factoring in the longevity of these systems versus that of a standard combi boiler. This combined with low running costs and the benefits to the environment mean it is reasonable to suggest that properly installed in the right situation there is no better alternative when it comes to sustainable heating for the home.
But, if space is going to limit your options for this particular renewable form of energy, take a look at what's involved with air source heat pump installation instead, and find out how to work out your energy needs and choose the right renewables to help future-proof your self-build or renovation.
