Reduce heat loss underground heating pipes

random.stranger

We have a condensing boiler in the shed with an 8m run of the pipes underground to the house.

We noticed on frosty days that the ground is thawed around the path of the pipes.

I dug up the pipes to find that the pipes were buried in normal pipe insulation, but not inside any sort of pipe to seperate them from the wet soil. The pipe insulation was compressed & wet from the ground.

I'm looking at two options:

1. Cut a 6inch wavin pipe lengthways & slip it over the existing pipes+ new insulation.

   I'm not sure if I will be able to pull the pipe apart enough to slip it over the existing pipes (2x 1" pipes + insulation over them.)

   I could close up the cut with some duct tape.

2. Open the pipes at a joint & put the wavin pipe over them + new insulation.

   I'm concerned this would introduce air into the system & I'm not sure if that could cause a problem with the boiler.

I've dug a hole 2-3 foot under the pipes at the middle of the trench & will fill it with stones etc to help the trench drain away in the winter months.

Anybody got any experience or insight they could share on this one?

I've been looking at freezing the pipes before opening them, but it looks like it will be pretty expensive to freeze 4x 1inch pipes & I could forsee it going horribly wrong in this hot weather.

The Continental Op

Some form of ducting. Insulation around pipe then vermiculite to fill the rest of the space.

What I have seen done is a base of flagstones 3 brick course either side and flags again on top. Insulation in bottom then pipes with the thicker insulation and filled with vermiculite.

One Idea that does occur to me is to use drain channels like this

one for each pipe (?) + pipe insulation and fill with vermiculite. Add drainage holes to the bottom and lay the drains on a bed of gravel. Put some builders plastic over the top before putting the grating on.

Mad idea but might inspire some better ones.

RainInSummer

Is swapping out the pipes and option?

https://www.pipelife.ie/plumbing-systems/plumbing-heating-pipes/district-heating-pipe.html

That said I'm not sure if they do the diameter you need. Doesn't look cheap but it might give ideas.

zidac

https://www.boards.ie/discussion/2058258472/reduce-heat-loss-underground-heating-pipes

Is it an option to create a boiler hut by the outside wall? as regards freezing i would just drain. If you close the rads both sides you will just drain the boiler and some pipes, the water will stay in rads. Is it an open or closed system?

random.stranger

https://www.boards.ie/discussion/comment/119461828#Comment_119461828

That would be ideal, don't know if it is within budget, will check it out.

https://www.boards.ie/discussion/comment/119461839#Comment_119461839

Open system. Great idea with the rads, will definitely do that. Boiler hut isn't an option unfortunately. There's a back boiler & hot water cylinder too, would I need to do anything with them? The back boiler seems to heat the cylinder & rads. When condenser boiler was upgraded controls were put in for separate control of rads & hot water, so sounds like they are on two different circuits. It's the back boiler that has me confused.

zidac

https://www.boards.ie/discussion/comment/119461860#Comment_119461860

There is a valve each side of circulating pump for back boiler so if you turn off one of them with screwdriver and the back boiler will only lose about 10% of water.

I expect there are all on circuit as even if two circuits it is the same water so not a problem. The actual pipework doesn't hold that much water, it is in the rads and the boilers.

Lumen

Pour in a load of 2 part closed cell foam?

random.stranger

Thanks everyone for your input. So the draft plan is to:

1. Close all radiators at both ends

(noting rough rotation on non-knob end for rebalancing afterwards.)

2. Close valve at each heating circulation pump

3. Insulate pipes with 20mm armaflex

(good plumbers merchant can supply armaflex or district heating pipe, steered me towards armaflex)

4. Tape 3D printed spacers to pipes (to reduce surface contact area with wavin pipes & conduction)

5. Open 1" heating pipes, put in 6 inch wavin pipe along length & close 1" heating pipes.

6. Close ends of wavin pipes with 2 part closed cell foam insulation (the cheapest I can find is €60, if anybody can suggest somewhere to get it in small quantities for cheaper, please shout).

7?. I'm thinking of bulk buying vermiculite to put in around the outside of the pipe to aid drainage & add insulation.

8?. Weed barrier over vermiculite to prevent it clogging with mud run-off

9. Fill in soil.

10. Reverse all the plumbing work.

Will closing valve at circulation pumps prevent system trying to replace lost water from opening pipes, or should I turn off mains water also?

Any tweaks/opinions/feedback appreciated...

whizbang

I did similar job many years ago.

Its relatively easy to slice open a length of pipe insulation, and tape it closed around the pipe; no messing with draining and refilling. Use 19mm. Armaflex is more difficult, and the weight of the pipe will compress it more than the cheap stuff.

Build an enclosed channel around the pipes with offcuts of external insulation. plenty of leftovers available cheap. Ideally the black foam poly stuff. Even 50mm will make a huge difference. Cheap silicone will seal it watertight enough. vermiculite shouldnt be used outdoors, mostly useless anyway.

Also try to separate the flow and return as much as possible. no sense in keeping all that heat if its just going straight back to the boiler.

22mm + 19x2 + 2x50 = 160mm wide/high, if you separate the pipes with 50mm then its 270mm high/wide.

random.stranger

https://www.boards.ie/discussion/comment/119503537#Comment_119503537

Thanks, I think you're right about vermiculite. I read that it absorbs water, so not ideal as secondary insulation. We bought 2 tonne of 20mm pebbles to fill in around the pipes & give proper drainage to the soak hole.

The 6" wavin pipes have been delivered & I am happy to use them as the pipes are quite shallow & would be great for protecting them.

We were going to top up the system with fernox while we were at it, but the plumber's merchants nudged us towards Tec7 Plumb, as it would seal up any leaks aswell. I'm wondering while we're at it should we flush the system with mains water aswell, is that DIYable?

Plumber said a few years ago that the old rads (40+ years old & cold at bottom) wouldn't take a power flush, so I'm wondering if we should do a DIY flush while we're at it with mains water to tide us over for a couple of years & at least improve the rads a bit.

Furze99

Twas me, I'd avoid opening joints/ cutting pipes whatever, if not strictly needed.