Air source heat pumps vs ground source heat pumps

Heat pumps are an effective and energy efficient way to heat your home and hot water. They work by absorbing heat from the environment and transferring it to a fluid, which is compressed to increase its temperature. This heat is then transferred from the compressed fluid into the central heating system, to use for both heating and hot water.

The main difference between the two types of heat pumps is where they get heat from: air source heat pumps (ASHPs) absorb heat from the air whereas ground source heat pumps (GSHPs) absorb heat from the ground.

For more information, see our in-depth guide to find out how heat pumps work.

A lot will depend on your circumstances, but there are some factors that will make your decision between an air source and ground source heat pump simpler.

Considering a ground source heat pump?

Essentially, if you don’t have outdoor space available, you can rule out getting a ground source heat pump. Digging trenches or drilling boreholes is a pre-requisite for a ground source heat pump, so if you lack the outdoor space to do so, you’ll need to explore different options.

Installing a ground source heat pump can also be expensive: you’d need a budget of at least £20,000. There is funding to support depending on where you live, however, grant funding is unlikely to cover the full cost.

So why would you consider a ground source heat pump instead of a comparatively cheaper air source heat pump?

If you live somewhere that regularly experiences very cold air temperatures, the ground source heat pump might be more efficient. This is because ground temperature tends to stay warmer throughout the year. Whether it’s more efficient enough to justify the extra cost will depend on the temperature of the ground where you live compared to the air temperature.

Considering an air source heat pump?

If you think an air source heat pump might be better for you, there are still some things to think about, including:

• Space: do you have the space required?
• Budget: remember, there may be funding available to help.

Some factors are common to both air source and ground source heat pumps, including:

• The size of your house.
• Whether it’s a newbuild or existing house (installing pipework around an existing building can have design challenges).
• How much preparation work needs to be done for the conversion, such as whether you need a new electricity supply from your fuse box to the location of the heat pump.
• Whether the installer recommends upgrading radiators to help improve efficiency.

The cost of an air source heat pump is approximately £14,000

A ground source heat pump on the other hand can cost around £28,000. The additional cost for the ground source heat pump installation comes from the external work in the garden, where either trenches or a boreholes will need to be dug.

• Find out more about the cost of air source heat pumps.
• Find out more about the cost of ground source heat pumps.

The efficiency of a heat pump depends on the ‘source’ temperature. The colder the source temperature, the harder the heat pump must work. This means that where a house is located and the time of year can affect the efficiency of heat pumps.

Air source heat pumps take heat energy from the outside air. Air temperatures tend to fluctuate between -5°C to 25°C for most of the year.

• The coldest ever air temperature recorded in the UK was -27°C in Braemar, Scotland.
• The hottest ever air temp recorded was 40°C in Coningsby, England.

However, -5°C to 25°C range covers at least 95% of the year for most homes in the UK.

Ground source heat pumps extract heat from the soil, where the temperature doesn’t reach as high, but it also doesn’t drop below freezing. Mostly, the soil temperature will stay above 5°C throughout the year.

This means there are many points during the year when an air source heat pump will be more efficient than a ground source heat pump, because the air temperature is warmer than the ground temperature. However, when it gets really cold, a ground source heat pump can be more efficient than the air source heat pump.

Unlike a ground source heat pump, an air source heat pump doesn’t need to use energy to pump fluid around the pipework outside. As a result, an ASHP can still be slightly more efficient on days there the air is the same temperature as the ground.

Overall, ground source heat pumps tend to be more efficient over the year if you live somewhere that often has very cold winter temperatures. Whether the energy savings will outweigh the additional installation cost will depend on where you are in the country, the ground temperature and expected air temperatures.

An air source heat pump can continue working at temperatures of around -15°C; some can even work at much lower temperatures. However, if the temperature is regularly below freezing, you might find that a ground source heat pump is a better option.

Air source heat pumps and ground source heat pumps may work in a similar way, but they have different setups and requirements.

Both could help you cut energy costs and heat your home efficiently and effectively, as well as reduce your carbon emissions.

If you’re limited by budget or space restrictions, an air source heat pump is more likely to suit you.

Any potential installer should be able to discuss all these issues with you in more detail to help you find the right solution for your needs.