Ground source heat pumps (GSHPs) harness natural heat from the ground for your home's heating system. Buried beneath the ground on your plot of land, these systems make use in the slight variation in temperature of the earth to supply your home with heating and hot water.
As you might imagine, installing a ground source heat pump is quite a disruptive job. It requires either digging large trenches across a larger plot of land, or digging a deep borehole to house a vertical heat pump array — both costly operations. This means that a GSHP isn't right for every kind of home, but for the right one, it's a renewable tech that's hard to beat.
Get to know more about how ground source heat pumps work with our in-depth guide, as well as the important matters such as how much one costs and how you may be able to claim some of the expense back through government grants.
(MORE: Get a quote for your heat pump)
What is a Ground Source Heat Pump?
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Ground source heat pumps use a series of buried pipes buried that extract the energy from the sun that warmed the ground. The heat pump then amplifies that energy into heat useful in the home.
There are two main elements of a ground source heat pump system:
- The ground array, which can be either a horizontal grid of pipes, which should be 1.2m below ground level, or two or three vertical boreholes, which are likely to be more than 70m deep. In either case the extent of the ground array will be determined by the size of the heat pump and the soil conditions
- The heat pump itself, which is installed in the house. Some of these include a hot water cylinder and can be the size of a large filing cabinet. The smallest pumps, such as those in the Kensa Heat Pump range, can be fitted in an under-sink kitchen cupboard, however, they're often located in dedicated plant rooms for easy access.
Ground source heat pumps use electrical energy in a highly-efficient way to produce heat, significantly reducing heating running costs and CO2 emissions.
While ground source heat pumps require electricity to operate, they can also be combined with renewable electricity sources such as solar PV panels.
Pros and Cons of Ground Source Heat Pumps
What are the Advantages of Ground Source Heat Pumps
- Running cost is likely to be around 45% lower than for a gas boiler, while also significantly less expensive than other renewables, including air source heat pumps.
- 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. You could also consider running a ground source heat pump along with solar PV panels to provide electricity for the heat pump.
- Once initial issues are dealt with you will have a heating system that is as reliable as a gas boiler and likely to last twice as long.
- There are grants available to offset the cost of ground source heat pumps.
What are the Disadvantages of Ground Source Heat Pumps
- The installation phase and start with the high capital cost — likely to be £8,000 to £10,000 for a typical 3 or 4 bedroom house
- There will be significant disturbance to the garden to install both a horizontal or vertical ground array.
- You'll also need to factor in the cost of upgrading your home's insulation, if required, as well as the cost of replacing radiators for low-flow versions or underfloor heating.
Replacing a Gas Boiler with a Ground Source Heat Pump
"Heat pumps operate at low temperatures which are much lower than the high system temperatures associated with oil boilers. Therefore, to help a heat pump work both efficiently and effectively, high levels of insulation ideally need to be in place so that any heat loss from the property is minimised," says Neil Sawers, Commercial Technical Manager at Grant UK.
Many older properties are not airtight and have sub-optimal levels of insulation, resulting in lower efficiency and resultant higher running costs. This means a requirement to spend on upgrading the insulation and airtightness of the property before installation of a ground source heat pump can be considered.
The cost of installing a heat pump system will be complicated by the difficulty and disruption involved in digging up a large area outside and running new pipework from the outdoor ground loop manifold to the heat pump unit in the plant room.
On top of this, you may also require new pipework to the hot water cylinder, possibly in an upstairs cupboard and also requiring replacing, and to the central heating distribution which may be located near the existing boiler rather than near the proposed location of the heat pump unit.
Even if you have a wet radiator system already, you may need to upgrade the size of the radiators to accommodate the low flow temperatures of a heat pump system to ensure it runs efficiently.
Is a Ground Source Heat Pump Worth it?
Depends on your point of view. Many find the high capital cost unpalatable. Others find the low running costs, high RHI payments, longevity and low CO2 emissions highly attractive.
It is reasonable to suggest that properly installed in the right situation there is no better alternative.
Types of Ground Source Heat Pumps
A horizontal ground array will be either straight pipes or coiled (known as slinkies). There is no technical or efficiency difference between these and the installer (together with the manufacturer) will advise which is best for your situation.
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.
For instance, 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 and can be prohibitively expensive.
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 efficiency of the heat pump.
Heat pumps are generally installed close to an external wall to give easy access to the ground array pipes. There will also need to be space for a hot water cylinder but as they are very quiet in operation they generally sit comfortably in a utility room.
How Much Does a Ground Source Heat Pump Cost?
How Much Does a Ground Source Heat Pump Cost to Buy?
A basic ground source heat pump costs between £2,000 to £15,000 depending on size and brand. This cost is likely to be three to four times more expensive than a gas combi boiler and double the cost more than an air source heat pump.
The quality of the heat pump equipment can add a significant amount to the cost of materials, effectively doubling it in some cases.
Top end heat pumps can have higher quality components and complex on board software for controlling and monitoring all aspects of the heat pump operation and also more costly alloys are used in the construction of the cases and components
The ground loop and installation complimentary systems (such as underfloor heating and radiators), as well as other peripheral materials, can substantially add to the cost of a ground source heat pump system.
A 200m2, four-bedroom house, built to Building Regulations standard, is likely to need an 8kW heat pump, costing around £6,000-£7,000, the balance being the installation cost which can vary significantly with the ground conditions.
A biomass boiler, another renewable alternative, can cost anywhere from £11,000 to £25,000.
Editor's Note: Homebuilding.co.uk partners with the UK's best heat pump specialists to match your requirements with their products and services. Simply answer a few questions on what you need from your heat pump and we’ll put you in touch with a suitable partner.
How Much do Ground Source Heat Pumps Cost to Install?
The complexity of the installation, including the distance from the heat pump unit to the ground loop manifold chamber will add to the installation cost.
Bigger properties will need larger heat pumps, even possibly more than one unit, alongside a more complex hydraulic design.
Horizontal ground array ground source heat pump
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 then connect the manifold to the heat pump unit in the plant room.
The cost of a horizontal ground array will depend a lot on the ground conditions. A very wet environment will possibly require pumps to clear the water in a trench while the pipes are laid. The walls of the trench could also be unstable which will require further support and a resultant cost increase.
If there are a lot of rocks in the ground then this will also add cost to the excavation.
The cost of the pipework for a 500m2 ground loop is around £2,000 and the cost of the excavation could be around £300 per day for a digger driver and £300 per week for the digger. Allow around £4,000 – £6,000.
The complete ground source heat pump installation for a 240m2 home will range in cost from around £15,000 to £25,000.
Borehole/vertical ground source heat pump
Borehole collectors are more expensive than horizontal ground loops. When done properly with a geologist report, it will cost around £100 per meter. There will usually be around 10 meters of borehole per kW so a 12kW heat pump will need around a 120 meter borehole or two 60 meter boreholes.
The overall cost, with the pipe installed and properly backfilled with the correct grout (often Bentonite clay), will be around £12,000.
Additional Costs When Retrofitting a Ground Source Heat Pump
With the potential costs of replacing radiators and fitting additional insulation to improve your home's fabric enough for a ground source heat pump to be a viable option, the overall cot of installation will increase dramatically.
Pipework and materials can be planned in early but the amount of disruption to the fabric of the building and requirement to change existing emitters could all contribute to the increased costs. This could see overall installation costs grow to around £35,000.
Anticipate that there may be a cost in removing the existing boiler. Where replacing oil or LPG heating fuels, there will also be a cost to remove the fuel storage tanks, concrete base and fuel pipework.
What are the Running Costs of a Ground Source Heat Pump?
In a property with an annual heat load of 15000kWh, you would expect the electric use to be somewhere between 3600kWh and 4700kWh. Based on the cost of a unit of electricity at around 15p per kWh and the average efficiency of a ground source heat pump at 320% to 420%, this represents an annual running cost of between £540 and £700.
These are the approximate costs of using different heating fuels in comparison:
- Oil: between £500 and £1,250 per year.
- LPG: between £825 and £1,320 per year.
- Natural gas: between £660 and £825 per year.
That compares to £890 per year to run a gas boiler and around £750 for an air source heat pump.
Load-Shifting Ground Source Heat Pumps
Load-shifting is a strategy for managing energy use by shifting from peak hours to off-peak hours where the energy source costs less. Ground source heat pumps are a prime candidate for applying load-shifting strategies, as they can run at off-peak times with ease, lowering the cost of the electricity it requires to run.
This is because:
- They're quiet, meaning they're unlikely to cause disturbance if active during the night, for example
- Ground temperatures stay pretty consistent throughout the day
All heating products make some noise, but heat pumps are usually quieter than fossil fuel boilers. A ground source heat pump may reach 42 decibels. A modern boiler should be around 40 - 60 decibels.
Ground source heat pumps with smart controls are able to create a heating schedule based on predicted electricity tariffs, meaning taking advantage of the lowest cost, lowest carbon electricity doesn't require manual operation of the heat pump unit.
Advances in technology, which include heat storage batteries, also mean that you can save any heat generated during these off-peak times for use during peak hours of the day.
How Much Money Could I Save by Installing a Ground Source Heat Pump?
The running cost of a ground source heat pump that will be around 3.4p/kWh, while a gas boiler is around 6p/kWh (as it will vary with different suppliers and assuming 90% efficiency) and an air source heat pump will be around 5p/kWh
How much you actually save will obviously vary with how much heat the house needs. Energy company Igloo estimates that you could save as much as £3,000 over the course of seven years.
What Grants are Ground Source Heat Pumps Eligible For?
There are several heat pump grants around the UK which can be used to recoup the cost of installation of a ground source heat pump.
Ground source heat pumps qualify for the government’s Renewable Heat Incentive, which will close to new applicants on 31 March 2022.
Under this scheme, those with renewable heat-generating technologies are paid back for the heat they produce.
The payments available for a ground source heat pump through RHI are a lot higher than for an air source heat pump, but this reflects an installation cost which is also potentially a lot higher. The RHI scheme will pay 21.16p/kW for each kWh of heat produced by the heat pump (less the electricity used to produce it), compared to 10.85p for air source and, of course, nothing for a gas or oil boiler.
Applications for the domestic RHI for eligible ground source heat pumps are still open for applications until 31 March 2022.
As of 1 April 2020, the rate for domestic ground source heat pumps is 21.16p/kWh payable quarterly for seven years from the date of commissioning.
RHI payments are for the renewable element of the heat produced, not for the electricity used to produce it.
Using the example of a four-bedroom house, likely to need around 11,000kWh of heat for space heating and 4,000kWh for domestic hot water, with an assumed SCoP (Seasonal Coefficient of Performance) of 4.5, the property will require 3,334kWh of electricity to run it.
In the scenario above, we need 11,000 + 4,000kWh of heat, less the 3,334kWh of electricity used.
RHI applies to 11,666kWh at 21.16p/kWh, meaning payments of £2,468 per year for seven years in this example.
How Do Ground Source Heat Pumps Work?
A mix of water and anti-freeze is pumped around the ground array 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 amount of heat that can be collected will be dictated by the soil conditions — for example, clay holds more heat than sand — and the amount of unshaded land available.
The loudest ones would be around 42 decibels, equivalent to a chest freezer.
As a rule of thumb an area of 50m2 is needed for each 1kW of heat output; an 8kW heat pump will need 400m2, assuming damp clay soil (a tennis court is 260m2).
A good installer will calculate the exact amount of heat needed for the house to determine the size of the heat pump needed.
They will also 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.
What Size Ground Source Heat Pump Do I Need?
Big enough to heat the house, and no more. 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, 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.
How are Ground Source Heat Pump Pipes Installed?
No, it's not advisable, for two reasons. Installing both the heat pump and the ground array are technically complex task, best left to properly trained and experienced people. And, to qualify for RHI the system must be installed by an MCS-accredited supplier.
For a horizontal ground array:
The pipes in the ground (the ground array) can be either straight or coiled pipes (slinkies). There is no technical or efficiency difference between the two and the choice will be dictated by practical on-site issues.
In either case the pipes will ideally be 1.2m below ground level. As important as 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.
That is 3m for straight pipes and 5m for slinkies (assuming clay soil, wider for other soil types). In addition, pipes need to be at least 5m from the boundary with any adjoining property.
For a vertical, or borehole system:
These will be anything from 70m to 120m deep, depending on the ground conditions and the size of the heat pump. As will the number of boreholes needed.
As the temperature of the ground rises with depth it is often advantageous to have fewer, deeper boreholes, but that is not always possible.
Do I Need Planning Permission to Install a Ground Source Heat Pump?
If the property is in a conservation area or overlooked by a listed property, it is wise to consult the appropriate authorities.
How Efficient are Ground Source Heat Pumps?
Efficiency is stated as the SCoP and a typical figure for a ground source heat pump would be something over 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 that make heat pumps a good idea.
The key issues to low running costs and high efficiency are:
- A well-insulated house will need a smaller heat pump, a smaller ground array (or fewer boreholes) and less electricity, reducing capital and running costs. System efficiency therefore starts with minimising the amount of heat required in the house
- A well-designed system — 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’, 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.
It has to be accepted that installing a ground source heat pump is not a DIY project.
It is a technically complex task that requires trained and experienced people. In addition, to qualify for RHI the installer and the equipment need to be MCS certified.
The key to all this 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. The indicators of a good installer would be someone who checks the soil conditions and offers quality equipment.
But it 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.
Radiators are designed to work with the high flow temperature available from a gas or oil boiler – usually something over 70°C. Heat pumps are most efficient with a flow temperature below 45°C.
Heating systems usually cycle – switch on and off – as the room cools and more heat is needed. The generally accepted solution is to increase the size of the radiator (probably double) so that the room is heated in a reasonable period of time.
There is a school of thought, now gaining some traction, that suggests that even at 45°C the radiator will eventually warm the room, and that if the heating system is run 24/7 the room will not cool and bigger radiators are not needed.
And as the system is still putting in the same amount of heat there is no effect on running costs.
(MORE: How to Replace a Radiator)
What Maintenance Does a Ground Source Heat Pump Need?
Heat pumps are not maintenance free, 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 – pumps and motors – and to ensure no refrigerant has leaked.
Cost is likely to be £100 to £150 per year.
Is a Ground Source Heat Pump Right for My Home?
If you are considering a ground source heat pump, bear in mind:
- A heat pump works best in a well-insulated home. A heat pump would still work in a home with a high heat demand will but it would be more expensive. The point is that the difference in price between a, say, 15kW and 30kW gas boiler might be £1,000, including installation. The difference between a 10kW heat pump and a 20kW might be £10,000, plus the extra installation costs. Investing in insulation has a significant impact on the cost of the GSHP.
- A horizontal array needs enough garden space. That said, a borehole installation is an option for those short on space. You will also need to consider access to the site for excavation machinery
- It will need to be paired with a suitable heating system and is most efficiently paired with underfloor heating as this requires much lower water temperatures than radiators. The alternative is to upgrade existing radiators to cope with the lower flow temperature
They offer a high RHI return, low running and maintenance costs and systems are more reliable than a gas boiler and longer-lasting. The question is perhaps not “is my house suitable for a heat pump” but rather “how do I make my house suitable”?
Can Ground Source Heat Pumps Provide Cooling?
Some ground source heat pumps can be optimised to also provide passive cooling to your property with the addition of some extra modules. Just as a ground source heat pump uses the natural warmth of the earth to heat a home, a ground source heat pump being used for passive cooling uses the temperature difference between the earth and the inside room temperature.
This is achieved by using systems such as fan coils or passive beams, passing the fluid of the cooling system through a plate heat exchanger with the ground array fluid passing through the other side.
Some air source heat pumps also include a reverse cycle modes, which can be used to provide active cooling through air conditioning.
Tim is an expert in sustainable building methods and energy efficiency in residential homes.
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