Ground source vs air source heat pumps - how do you choose?

So you’re considering a heat pump - that’s what we like to hear! The more that people understand the benefits a heat pump brings to your home, the more we can tackle the huge issue of climate change, meet our net zero targets - while living a life that is better for the environment and healthier for us all over all.

When setting out to choose a heat pump, the first thing you need to understand is that there are two types: air source and ground source. In this article we shed light on the differences between them and the benefits of each so you can decide which one is better suited to your home.

What’s the difference between ground source and air source heat pumps and how do they work?

The main difference between air source and ground source heat pumps is the source of heat they use:

• Air Source Heat Pumps (also known as ASHPs) extract heat from the surrounding air, even in cold temperatures
• Ground Source Heat Pumps (also known as GSHPs) extract heat from the ground, which remains at a relatively constant temperature throughout the year

ASHPs work by circulating a refrigerant through a heat exchanger that absorbs heat from the air. This heat is then transferred to the indoor air, providing heating and cooling. GSHPs use a system of pipes buried deep underground to circulate a fluid that absorbs heat from the ground. This heat is then transferred to the indoor air, providing heating and cooling.

It’s not hard to see the immediate difference, and possibly the most immediate problem between the two: air source heat pumps are a contained unit resembling an air conditioning unit (in fact, the technology is the same, just in reverse) and ground source heat pumps require lots of piping dug deep into the ground in order to extract the heat. The depth the rods need to go depends on whether they use a horizontal (1-2m) or vertical ground loop (60m depth, minimum, but usually over 100m or more). The latter is usually used when space is limited, and the former when there is enough outdoor space to house a unit next to your house.

Ground source heat pumps: main factors & benefits

As you can probably tell, the differences between the two heat pumps are stark - so what are the main benefits of a ground source heat pump?

• GSHPs are more efficient and inaudible
• They are typically more expensive to install
• They require significant groundworks, which may not be possible for all properties

Air source heat pumps: main factors & benefits

Let’s move onto air source heat pumps. In general, air source heat pumps:

• Are usually less expensive to install
• Require less space, making them a good option for many homeowners
• Can be less efficient in extreme sub zero colder climates (but air source heat pumps are still 3-5 times as efficient as a gas boiler – see here for more details https://www.thermly.co.uk/articles/how-efficient-are-heat-pumps)

Which will be right for your home?

Choosing between an air source heat pump and a ground source heat pump depends on several factors, including your specific needs, budget and the suitability of your property for each type of system.

When setting out on researching and choosing the right one for your home, it's important to understand what you want, what’s important to you and what your home is capable of hosting. To determine which heat pump is best suited for your home, consider the following:

1. Space and ground conditions:

• ASHPs: Require less space and are easier to install
• GSHPs: Need significant ground space for horizontal loops or borehole drilling, which can be challenging in urban areas with limited space

2. Budget:

• ASHPs: Generally less expensive to install than GSHPs – often significantly so
• GSHPs: Higher upfront costs due to groundworks and drilling

3. Aesthetics:

• ASHPs: Outdoor unit can be considered visually intrusive for some
• GSHPs: Ground loops are mostly hidden underground

Conclusion

In summary, when it comes to choosing which heat pump is best for your home, we would advise talking to an expert who can visit your home and advise accordingly. However, for most homes the better option is likely to be ASHP unless you have significant ground space and budgets – in which case you can benefit from the incredible efficiency offered by a GSHP

We’re here to help you choose the best heat pump for your home and then support you along the installation journey.

• Take our Heat Pump Readiness test to determine how heat pump ready your home is: https://platform.thermly.co.uk/heatpump-readiness
• Talk to our team today! We’re here to help you decide what the best heat pump is for your home and help you take the first step to more efficient and sustainable living: https://www.thermly.co.uk/contact
• For further reading on all things heat pumps, head to https://www.thermly.co.uk/articles

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