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Surface mount or bury primaries for heat pump installation?

 
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Air Source Heat Pumps (ASHPs)
Last Post by pash44pump 3 weeks ago
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 tomasmcguinness
(@tomasmcguinness)
Trusted Member Member
Joined: 2 years ago
Posts: 31
Topic starter 29/06/2025 9:52 am  

What about those pipes that include conduits for electrical cables such as Isoflow or Uponor?

 


Owner of a ridiculously oversized 35kW boiler and trying to make it as efficient as possible. 4.8kW solar PV with 5.4kWh storage. EV driver.
Follow my journey at https://www.youtube.com/@tomasmcguinness
Heat pump installation has started!


   
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Transparent
 Transparent
(@transparent)
Illustrious Member Moderator
Joined: 5 years ago
Posts: 3342
29/06/2025 3:17 pm  

Can we have some links to those you're considering please @tomasmcguinness ?!

I think we're basically going to say "follow the manufacturer's instructions",
but it would still be good to check out what those are.


Save energy... recycle electrons!


   
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Aventus Eco
 Aventus Eco
(@aventus-eco)
Active Member Member Professional+
Joined: 1 year ago
Posts: 7
01/07/2025 10:17 pm  

@tomasmcguinness, I think your best bet would be using underground ducting. You can get pre-insulated pipe for the flow and return, plus an additional two ducts, one for the power cable and one for the data cable.

At the ends, when everything comes up out of the ground, you can use press fittings to connect onto copper or, even better, insulated MLC pipe. If you go with copper, just make sure you insulate it properly with something like Primary Pro.

There are a few different manufacturers out there, but City Plumbing stock the ducts… you just tell them the length you need, and they’ll cut it to size and can do next-day delivery.

Also, make sure you get the proper end seals where the duct exits the ground. You basically heat it up with a heat gun and it seals the duct tight around any pipes, just like electrical heat shrink. It’s dead easy.

As for depth, 600mm is standard guidance to protect from frost and spade damage, but if you're struggling with that, going a bit shallower isn’t usually a big issue. Frost isn’t a real concern here since your flow and return will be in an insulated duct, unlike a mains water pipe. attached are some links and install guidance PDF.

Pre-Insulated Underground Pipes

INS140-3225-2HSC - Pre Insulated Pipe 140mm x 25mm or 32mm Heat Shrink Cap | Polypipe

pre-insulated_installation_guide_0.pdf


   
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 tomasmcguinness
(@tomasmcguinness)
Trusted Member Member
Joined: 2 years ago
Posts: 31
Topic starter 29/06/2026 9:37 am  

Quick update on this - it's been quite a long time as progress got delayed due to weather and other priorities!

I ended up with 40m of Microflex UNO pipe. Enough for 18m of flow and return. https://www.watts.eu/en-gb/products/eu/microflex-pre-insulated-piping/pipes-for-heating/1-microflex-uno-6-bar

image

I managed to get most of the trench down a depth of 50mm, but in some parts it's only 20mm, due to waste pipes.

image

It was tough going and I had to replace two sections of pipe, which I "disturbed" 🤬 

I added three SWA cables. Power for the heat pump, control for the heat pump and an addition 2.5 for a garden socket (I'm only digging one trench!). Back filled it and added warning tape.

image

Over the weekend, I shuttered and poured the concrete for the base. I use 12mm hardwood ply and some 2x4s. My wife mixed 0.2m³ of concrete - 22 bags of Blue Circle multi-purpose concrete with Siteworx screed fibres.

image

Electrician should be coming in the next week or two to get the new circuits wired up and plumber shortly after to take out the boiler and upgrade the plumbing!

Feels like I'm almost there!

 


This post was modified 4 weeks ago by tomasmcguinness

Owner of a ridiculously oversized 35kW boiler and trying to make it as efficient as possible. 4.8kW solar PV with 5.4kWh storage. EV driver.
Follow my journey at https://www.youtube.com/@tomasmcguinness
Heat pump installation has started!


   
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bobflux
 bobflux
(@bobflux)
Estimable Member Member
Joined: 5 months ago
Posts: 139
02/07/2026 4:26 pm  

Watts Microflex Duo, intended for burial, about 45€/m, with 2x 26/32mm Barrier PEX.

It is quite stiff and difficult to manoeuver but it does the job.

 

image

 

 



   
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 tomasmcguinness
(@tomasmcguinness)
Trusted Member Member
Joined: 2 years ago
Posts: 31
Topic starter 02/07/2026 5:36 pm  

@bobflux That's the stuff. The installer recommended two individual pipes as they have a smaller turning radius. I found the sun's heat to be very helpful when bending it into place.


Owner of a ridiculously oversized 35kW boiler and trying to make it as efficient as possible. 4.8kW solar PV with 5.4kWh storage. EV driver.
Follow my journey at https://www.youtube.com/@tomasmcguinness
Heat pump installation has started!


   
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 pash44pump
(@pash44pump)
Trusted Member Member
Joined: 11 months ago
Posts: 70
08/07/2026 12:41 pm  

@abernyte seconded. Used to be good friends with my neighbour until I installed solar on the roof facing his garden (fully discussed and agreed) which led to a big falling out afterwards because he didn't like the look of them. Be very wary of using neighbour's wall.



   
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 tomasmcguinness
(@tomasmcguinness)
Trusted Member Member
Joined: 2 years ago
Posts: 31
Topic starter 08/07/2026 12:45 pm  

@pash44pump I'm glad I made the effort to dig the trench. It's a much tidier job when nothing is visible.


Owner of a ridiculously oversized 35kW boiler and trying to make it as efficient as possible. 4.8kW solar PV with 5.4kWh storage. EV driver.
Follow my journey at https://www.youtube.com/@tomasmcguinness
Heat pump installation has started!


   
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 pash44pump
(@pash44pump)
Trusted Member Member
Joined: 11 months ago
Posts: 70
08/07/2026 12:50 pm  

@tomasmcguinness Spot on



   
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