Most modern or newly built properties are well insulated and primed for installing heat pumps.

This is because heat pumps are currently one of the most efficient and eco-friendly heating solutions and fit with the UK Government’s ‘green revolution’ plan along with hydrogen-ready boilers, which are really and logically the only viable long-term solution.

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Choosing between air source heat pumps & ground source heat pumps

Heat pumps are a good option, therefore, there is room for the conversation to shift to which is the better option between air source and ground source heat pumps (ASHP vs GSHP) for your building or project requirements.

These are the 2 options you get for heat pumps, and both have strengths and limitations depending on your specific circumstances.

We know that the housing spectrum in the UK is vast; it could be an old building, a new development, a tight fit, an expansive property, among other variables.

Keep reading if you are looking for impartial advice about the best technology or system suited for your project.

Air source vs ground source heat pump – How they work

The main difference between heat source and ground source heat pumps is how they transfer thermal energy to heat your home.

Air sources heat pumps take heat from the air, whereas ground source heat pumps take thermal energy from the ground.

Heat pumps are taking over the UK’s heating systems because they use sustainable and renewable naturally occurring heat to provide hot water and heat your spaces.

They are electrically driven, which means they can even be powered by renewable energy sources like solar panels, further cleaning the energy. This is all achieved at a fraction of the cost you would have incurred with oil or propane.

However, there are differences between air source heat pumps and ground source heat pumps in terms of requirements, setup, and how they work that we should clarify to give context to our comparison.

Air source heat pumps (ASHP)

These pumps extract heat from outside air as their name suggests and heat water and power the space heating system. The pumps are installed outside the building, making it easier to capture air.

A fan draws in the air with thermal energy and passes it over a heat exchanger that contains an energy-absorbing fluid.

The fluid is then transferred to a compressor which heats it to the required temperature, after which it is distributed to your hot water tanks, underfloor heating, and radiators to heat your water and space.

On hot summer days, the reverse is applied; the heat from inside the room is transferred to the air outside using the same process, effectively cooling the room.

Ground source heat pumps (GSHP)

They draw their energy from beneath the surface of the ground or earth to power your heating and heat water. They are typically installed inside the building and connected to loops of pipes containing the energy-absorbing fluid buried underground.

As the fluid circulates through the pipes, it absorbs thermal energy from the ground. It passes through a compressor which raises its temperature to what is sufficient for the building’s needs.

It is then distributed to your hot water tank, underfloor heating, and radiators to provide hot water and heat. They rely on the consistency of the temperatures underground to heat or cool your spaces which we shall realize is a great advantage later on.

Comparing the efficiency of air source vs ground source heat pumps

Heat pumps are more efficient than other heating systems because they don’t generate but rather concentrate natural heat so it can be applied to our heating needs. T

There is still a difference in efficiency between ASHPs and GSHPs that is mainly attributed to the heat source as an alternative to gas boilers

Air source heat pump efficiency

Their efficiency rating averages 300%, meaning every kW of electricity can produce 3kWh of heat. Because they rely on outside air, which is subject to the ambient temperatures, the efficiency can be hampered during winter or when the temperatures are low.

The system needs to work harder to deliver the same heating requirements when the climate is freezing and uses more electricity.

They can provide a wider temperature range than GSHPs because they can go as low as -15°C, but they are more efficient in warmer temperatures which are hardly consistent in the UK.

Ground source heat pump efficiency

GSHP’s efficiency ratings often go up to 400%. The heat is transferred underground through the movement of the energy-absorbing fluid. The liquid retains approximately four times more heat than air, and the ground cover offers additional insulation.

They are also not susceptible to temperature fluctuations due to climate changes as the underground temperatures are relatively consistent throughout the year. They can keep the building warm in the middle of winter without compromising efficiency.

Most of the UK’s underground temperatures at the level where the pipes are laid (1 to 2m underground) hardly stray beyond the confines of 8.8°C and 12.7°C. The soil is heated during summer by the sun and will retain the heat through winter.

GSHPs are more efficient than ASHPs, estimated at 20%, making them cheaper to operate. Nonetheless, a decent ASHP system will efficiently cater to all your heating and hot water needs at a lower premium than fossil fuel-powered systems.

Associated costs of air source vs ground source heat pumps

The purchasing cost of a heat pump is a factor of its heat output capacity, size, make, model, and brand. Your pump selection will also determine the cost of material and associated parts needed to complete the system.

ASHPs are generally cheaper than GSHPs. The price range for ASHPs is between £4,000 and £11,000 while that of GSHPs is £8,000 to £12,000.

This gap between the prices of the actual pumps is not even as significant as the one between their installation costs. ASHPs are much cheaper to install than GSHPs.

Air source heat pump installation costs

Installation costs will range between £8,500 and £15,000 because the process can be completed within two days, is straightforward, and is not labour-intensive. These are ballpark figures. The actual costs will vary depending on your circumstances and specific contractors.

You can however get air source heat pump grants in the UK towards installation costs of up to £5,000

Ground source heat pump installation costs

Ground source heat pump costs are much higher than air source. installations are more technical and require specialists who charge a higher premium for their services.

They are not single units like ASHPs and require pipework that involves excavations and landscaping, which drives the costs higher.

There are two possible GSHP configurations with different installation requirements that impact installation costs differently.

• Horizontal loop configurations involve digging shallow trenches (1 to 2m deep) on wider surfaces and laying the pipes horizontally. Because of the added excavation charges, laying of pipes, and additional labour, the process will cost between £15,000 and £20,000.
• Vertical loop configurations require digging of boreholes for the piping to be laid vertically. These holes run deeper, and the drilling and laying of pipes require specialized equipment and personnel. The process can take up to a month to complete, and the overall costs range between £18,000 to £35,000 depending on the scope of the project

Renewable Heat Incentive (RHI)

The UK government offers payments over seven years to people who have installed heating systems that use renewable energy under the RHI scheme to make them competitive in relation to cheaper fossil fuel alternatives.

Both heat pumps are eligible for payments under the RHI scheme, which can go a long way in recovering the costs incurred during installation.

The RHI tariff is based on efficiency ratings, with the more efficient solution getting a higher rating. In this case, a GSHP system qualifies for a higher tariff, say 21.29p/kWh, while the less efficient ASHP might get 10.49p/kWh.

In seven years, the GSHP owner will have received £29,806, while the ASHP owner will have received £15,288.

These amounts almost cover the entire installation cost and, depending on the deal you got from your installer, can help you break even.

This structure makes a good case for GSHPs whose installation costs are way higher than ASHPs.

Comparing the installation process for air source vs ground source heat pumps

Air source pump installation process

ASHPs are straightforward to install, and the work can be completed within two days. This period is shortened significantly if the building has existing flues. The units are mostly fitted on rear-facing and side-facing walls.

You won’t require a lot of planning permits in most cases, but there are restrictions, especially concerning distance from neighbouring households. You should familiarize yourself with these rules, but your local contractor will be better placed to know them.

Ground source pump installation process

Installation of GSHPs, on the other hand, is a messy and complex affair. It can take anywhere between two and six weeks.

• Horizontal trenches involve excavating at least 100 square meters of your land up to two meters deep. The earth that has been dug up needs to be placed somewhere as the work continues until the pipes have been laid down, and it gets even worse if it rains.
• Vertical loops need boreholes that go at least 100 meters deep. While you will have more space for the excavated earth as you work, the process is more technical, and the drilling is noisy, so you need to alert your neighbours and apologize in advance. They have their own share of mud, dust, and water, which create a mess for the duration of the installation, and you will still require enough space for the drilling rig to access the site.

You can redo the landscaping afterwards on top of the piping to restore the outlook of the place or reclaim your garden.

ASHPs vs GSHPs – Which one allows the best utilisation of space and ambience?

ASHPs are installed outside, which means they don’t compete for the limited space inside the house.

This is an advantage for most buyers, although you need to ensure they are not too close to your neighbours beyond the approved distance in your region.

As much as they are insulated to minimize noise emission, ASHPs will hum, and some sensitive people might be affected by the humming.

You need to reserve space indoors for GSHPs. Smaller ones can fit underneath the stairs or in a cupboard, so they are out of the way, but they can be imposing if your heating needs require a powerful unit.

The components that need a lot of space are the ground collector pipes. You need substantial land for horizontal loops, but you can opt for vertical boreholes if you are pressed for space.

The redeeming element for GSHPs is that they are not visually intrusive once they are installed. The positioning of the pumps inside the building also means the neighbours won’t be offended in the long run, and they are silent and efficient.

Which is easier to maintain between an air source and a ground source heat pump?

Renewable heating systems generally require minimal maintenance. If properly installed, heat pumps will easily deliver between 20 to 30 years of service before replacement is necessary.

Annual service checks are necessary to confirm everything is in order. Annual service for an ASHP will cost approximately £150, while a GSHP will cost £190.

GSHPs typically last longer than ASHPs for a couple of reasons; The heat pump is housed within the building and is not subjected to external elements like extreme weather and vandalism, allowing extension of their lifespan.

They are also more efficient throughout the year, so they hardly strain to deliver.

Are heat pumps the solution and which is best?

All factors are constant, a horizontal loop ground source heat pump is the superior solution for heat energy.

It runs silently, has an extended lifetime, and is efficient all year round. It costs less than the vertical loop version to install but is entitled to the same RHI tariff.

In our opinion, the most logical and cost-effective way is to prepare for hydrogen. Once hydrogen can be produced cheaply, then this is only the viable solution to be able to provide most households in the UK with fuel.

But factors are hardly constant; each building is different, and so are the project requirements.

The available resources in terms of finances, expertise, and land also play a big role.

Consider your unique circumstances as you read through the above information to compare air source vs ground source heat pumps and hydrogen ready boilers.