What’s the difference between an air source heat pump and a ground source heat pump?

The government’s decision to reduce dependence on gas boilers by 2035, means that many households will need to look at alternatives at some point. Those alternatives include air source heat pumps and ground source heat pumps, but what’s the difference?

Here, we explore both options and look at how they work, what they cost, and what you should consider before installation.

What is a heat pump?

The basic function of a heat pump is to take heat from the environment around it and turn it into energy that can then heat your home and provide you with hot water.

Heat pumps create more energy than they use so they’re considerably more energy efficient compared to traditional fossil fuel boilers.

If you’re considering your options, you can choose between an air source heat pump and a ground source heat pump. The key difference between them is the heat source they use.

How do air source heat pumps work?

Air source heat pumps take the air from around it, drawing it through a fluid (called the refrigerant). This liquid is then compressed to increase its temperature, which is then used to heat your home and create hot water.

Air source heat pumps can extract heat from air temperatures as low as -15°C so they can be used almost all year round in the UK. If you live in a region that regularly dips well into the minus figures, you may need to consider a ground source heat pump (or other alternative heating system).

How are air source heat pumps installed?

One of the advantages of an air source heat pump is that they’re easier to install compared to a ground source heat pump. They just need to be positioned on the ground and next to a wall close to your house.

Air source pumps look similar to air conditioning units (and are about the same size). There should be a fair amount of space around it so that air can circulate freely.

If you opt for an air source heat pump, you can choose between a monobloc or split system.

  • Monobloc air source heat pump – as the name suggests, your heat pump is housed in one unit. The single unit which sits outside of your home transfers the heat to your radiators and water cylinder. Monobloc systems are cheaper and simpler to install as there is only one external unit.
  • Split system air source heat pump – instead of a single unit, the heat transfer element is separated into a second unit, which is then put inside your home. As this second unit sits within a warmer environment, it’s slightly more efficient as it doesn’t lose as much heat. However, as there are two units to install, split systems are more expensive. You’ll also need space inside the building to store the second unit.

When your home is assessed with an air source heat pump in mind, your installer should be able to recommend the most suitable system for your property.

How do ground source heat pumps work?

Ground source heat pumps draw the air from the ground, absorbing it into a liquid which circulates through a network of pipes that have been laid in your garden (or surrounding land). This passes through the refrigerant fluid and compressed to raise the temperature (as it is in an air source heat pump). A heat exchanger then extracts the heat and transfers it to your home through your radiators.

How is a ground source heat pump installed?

Ground source heat pumps use a series of pipes which are laid underground. If you have enough space outside, pipes will usually be laid horizontally across the land. If not, they can be arranged vertically in boreholes, but this type of installation can be slightly more complicated.

You’ll also need space inside your home to store the pump (usually the size of a large fridge).

Do heat pumps need to be serviced?

Ideally, you should have your heat pump serviced annually by a qualified engineer.

Is a heat pump noisy?

Air source heat pumps are slightly noisier than ground source but not much. It’s simply the noise of the fan as it circulates. Heat pumps don’t use an external fan so are generally quieter.

In reality, the noise generated shouldn’t interfere too much with everyday activities – for example, you should still be able to have a conversation at normal speaking levels. Just be aware that the harder the pump needs to work, the noisier it will be (so they can be louder in colder weather).

Do you need planning permission for a heat pump?

The good news is that ground source heat pumps are considered permitted development, so you don’t need planning permission. The rules are slightly different if you live in a listed building, or your home is in a conservation area. If either of these is the case, you’ll need to contact your local council to see what you’re allowed to do.

Air source heat pumps are also considered permitted development but only if you meet certain criteria. For instance, the pump unit must not exceed 0.6 cubic metres and it must meet standards set out in the microgeneration certification scheme (MCS). Your installers should be able to offer advice and let you know if you meet all the requirements for permitted development or if you need permission.

For more information about planning permission for heat pumps, head to:

Can a heat pump help reduce my energy bills?

A heat pump can help reduce energy bills but a significant factor in how much you save will depend on the system you’re replacing. Generally, the older or more inefficient your existing heating system, the more you’re likely to save.

Data from the Energy Saving Trust suggest you could save up to £2,200 annually on fuel if you replaced old electric storage heaters with a ground source heat pump. If you replaced a G-rated oil boiler, you could see savings of up to £1,000 or £560 if you switch over from an older G-rated gas boiler.^

Annual savings are slightly lower if you install an air source heat pump, up to £1,100 if you’re replacing old electric storage heaters. If you replace an old G-rated oil boiler, you could save up to £550 or £295 if you’re replacing a G-rated gas boiler.^^

How efficient are heat pumps?

Heat pumps use less energy compared to their output so they’re more efficient than traditional fossil fuel boilers or electric heaters.

However, the level of efficiency they reach will depend on the source temperature. The colder the air or ground, the harder the pump will have to work and the less efficient it will be compared to when the air or ground is warmer.

Also, as the air temperature in the earth is more consistent than air temperature, the heat generated by a ground source will usually be more consistent compared to an air source heat pump.

How much do heat pumps cost?

Neither option is cheap although an air source heat pump is slightly less expensive. As a broad guide, air source heat pumps cost in the region of £7,000 - £13,000, while ground source heat pumps can cost around £14,000 - £19,000. That said, some ground source systems are considerably more expensive, particularly if you need to dig boreholes and position your pipes vertically. In this instance, the Energy Saving Trust estimate it could cost up to £49,000.

To calculate cost, installers will need to consider:

  • The type and brand of heat pump you buy.
  • The size of heat pump you need (this will depend on the size of your home or property).
  • How it will be installed (setting pipes in boreholes for ground source pumps generally cost more than setting them horizontally for air source).
  • Whether you need to upgrade insulation in your home or your radiators.

Can I get government help?

Yes, you can apply for the government’s boiler upgrade scheme, which is designed to help households switch from fossil fuels to more sustainable energy sources.

To be eligible, you will need to meet certain criteria but if you do, you could get £7,500 to put towards an air source or ground source heat pump.

Where can I find more information about heat pumps?

There’s a lot to consider if you’re thinking about moving from traditional heating sources to a heat pump. While cost is likely to affect your decision, the space you have, and your location may also impact what’s available to you.

With that in mind, it’s a good idea to speak to more than one installation firm to get a clearer idea of what your options are (the Energy Saving Trust recommend that you get at least three quotes).

The Energy Saving Trust has also put together these detailed guides:

^Savings are based on a four-bedroom detached home that is well-insulated (https://energysavingtrust.org.uk/advice/air-source-heat-pumps/

^^Savings are based on a three-bedroom semi-detached home, https://energysavingtrust.org.uk/advice/air-source-heat-pumps/


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