Hi John,

I’d be wary of running the coils too tightly together. As you’ll know, a ground source heat pump loop extracts warmth from its surroundings. If two coils are laid too close to each other, they may both be extracting warmth from the same zone. That could lead to a temperature drop in the surrounding soil, which in turn would reduce the efficiency of the setup.

My understanding is that with horizontal loops the coils need to be at least 800mm apart, but obviously the best thing you can do is follow your manufacturer’s instructions, which should specify some guidelines for you according to the soil type.

We’ve put your question to a renewables expert so we’ll get a fuller answer to you soon!

In the mean time you might want to check out our guide on why you should consider heat pumps: https://www.self-build.co.uk/why-choose-heat-pumps

Chris, Deputy Editor, Build It magazine

The energy required by the GSHP system is extracted from the ground and then replaced by the sun. Therefore the surface area of ground is the critical unit.

As a rule of thumb for damp soil, I would place the pipes one metre apart (but certainly no less than 0.8m). Therefore you can use a bigger bucket on the digger and put the flow and return in one trench.

I personally would not want to use pipe lengths of more than 100m (150m at most) as the longer lengths are very difficult to manage, the risk of damage is greater and the pump sizes will need to be increased.

I would suggest you use a 1metre bucket and use either 6 x 50m trenches, 5 x 62.5m trenches or 4 x 75m trenches. Whatever you choose, the lengths of each loop must be the same and the trenches must also be a minimum of 0.8m to 1m apart.

For guidance on all of this check with your MCS registered installer or MCS guidance for heat pump installations: MIS 3005 v3.1a.

David Hilton, Heat Pump Manager at Samsung EHS

Hi John

If you are going to dig trenches 1.2m wide then it would be simpler to drop the coils in as a slinky array you can then fit 150m of pipe in a trench approx 1m x 1.2m x 40m. You need to leave 5m between trenches so you would require 4 x 40m slinkies which would fill a space 40m x 19m. This size of array should serve a heat pump of around 16Kw. If space is at a premium consider using boreholes a couple of 70m boreholes could suffice.
It is essential to size your loop correctly and to achieve that you must also look at the geology. I would advise you to allow your heat pump installer to size the loop and supervise the installation.

Regards Rob

MCS standards states that the space between loops should be a minimum of 0.75m. If the pipes are laid too close together the ground will not have enough thermal energy to support the heating requirement. This will lower the performance of the heat pump and could lead to the ground freezing.

Correct sizing, installation and commissioning is essential if the full benefits of a ground source heat pump are to be realised and I would therefore strongly recommend you engage a specialist contractor to advise you. It’s also important to remember that if you wish to take advantage of the RHI scheme, the installation and installer must be MCS certified.

Steve Keeton, technical director at Vaillant