Advice on insulating underground pipework

[Diablo]

All,

After years, we have decided to replace our internal Warmflow (total rubbish...) with an external Grant oil boiler.  It will be located about 1 metre from the house, so will need to run 22mm pipes out of the boiler, underground and up the side of the house.

 

I would really appreciate some advice on:

 

1. Is it best to use Copper of flexi pipe under ground?

2. What is the best way to insulate it?

3. Rather than drilling new holes for the pipes, I was thinking about using the hole for the existing boiler's flue. Any thoughts on how to seal up the hole once the pipes are in place?

 

Many thanks,

Rog 

[ProDave]

Combi or system boiler?

 

Why not, as is usually the case, stand the outside boiler so it sits against the wall where the old boiler flue used to exit?  Then you have completely eliminated any need for buried cables.

[Carrerahill]

I knew a guy who had a "boiler house" about 10 meters from his house. He ran 22mm flexi's fully insulated and foil wrapped etc. then the whole lot was run inside 4 inch soil pipe which he insulated then ran in a bed of gravel along a trench. Worked well. 

 

For 1 meter I would probably go a little over the top but it would work well. I would probably create a concrete/block channel, with a mini PIR insulated slab foundation, DPC round the lot, PIR insulation up the sides, insulate the pipes with good insulation, foil wrap them, then fill the whole trench with some sort of insulation fill, then PIR lid and a concrete slab or something over it. Sounds mad, but for 1 meter you really could do a seriously good job as costs would be acceptable to go "over board"

 

You can buy external heating pipe which is a big insulated pipe with both flow and return within it, but I doubt you could get a meter or so of it on its own, the termination process would probably be about as long as the run and the whole thing would not be worth it.

 

As for the old flue, I would make up the insulated pipes, pass them through then pack any free area around the pipes with off cuts of pipe and then fill the hole - that is standard practise for filling ducts and sealing them, basically your hole in the wall is a short "duct".

 

See sort of example here:

 

 

 

Edited February 28, 2019 by Carrerahill
spelling

[Diablo]

1 hour ago, ProDave said:

Combi or system boiler?

 

Why not, as is usually the case, stand the outside boiler so it sits against the wall where the old boiler flue used to exit?  Then you have completely eliminated any need for buried cables.

Hi, It is a System boiler.  It is a good point and was my first thought.  However, the issue is that there is a rainwater gully, manhole and grey water pipes all in close vicinity.  It could be done, but in order build a solid base for the boiler, I would need to somehow micropile around the various underground pipes.  I will have another think, as it does make it easier for power as well.

 

 

[Diablo]

1 hour ago, Carrerahill said:

I knew a guy who had a "boiler house" about 10 meters from his house. He ran 22mm flexi's fully insulated and foil wrapped etc. then the whole lot was run inside 4 inch soil pipe which he insulated then ran in a bed of gravel along a trench. Worked well. 

 

For 1 meter I would probably go a little over the top but it would work well. I would probably create a concrete/block channel, with a mini PIR insulated slab foundation, DPC round the lot, PIR insulation up the sides, insulate the pipes with good insulation, foil wrap them, then fill the whole trench with some sort of insulation fill, then PIR lid and a concrete slab or something over it. Sounds mad, but for 1 meter you really could do a seriously good job as costs would be acceptable to go "over board"

 

You can buy external heating pipe which is a big insulated pipe with both flow and return within it, but I doubt you could get a meter or so of it on its own, the termination process would probably be about as long as the run and the whole thing would not be worth it.

 

As for the old flue, I would make up the insulated pipes, pass them through then pack any free area around the pipes with off cuts of pipe and then fill the whole - that is stndard practise for filling ducts and sealing them, basically your hole in the wall is a short "duct".

 

See sort of example here:

 

 

 

 

 

Brilliant! That is exactly the sort thing I was looking for.  I had a quick look online for the sealing compound, but came up dry,  It looks like an industrial solution, so my guess is that there maybe a minimum purchase requirement..  What about expanding foam, as an alternative? 

[ProDave]

4 minutes ago, Diablo said:

Hi, It is a System boiler.  It is a good point and was my first thought.  However, the issue is that there is a rainwater gully, manhole and grey water pipes all in close vicinity.  It could be done, but in order build a solid base for the boiler, I would need to somehow micropile around the various underground pipes.  I will have another think, as it does make it easier for power as well.

 

 

If it is a system boiler then it is just flow and return, and with enough antifreeze / inhibitor it will be good to well below freezing anyway, so not such a great problem.  My concern would have been if it had been a combi where you would have had potable cold supply and hot out, and there's nothing you can do to protect those other than insulation.

[Carrerahill]

12 hours ago, Diablo said:

 

 

Brilliant! That is exactly the sort thing I was looking for.  I had a quick look online for the sealing compound, but came up dry,  It looks like an industrial solution, so my guess is that there maybe a minimum purchase requirement..  What about expanding foam, as an alternative? 

It is a commercial solutions, as you would rarely see this in a domestic environment but it's easily done. They are just using MDPE pipe, anything that suits the materials, temperatures etc. will work, so in your case some off cuts of 22/15mm plastic pipe, then as for the capping/sealing compound this is just a semi-permanent polyurethane or silicone. The reason we say semi-permanent is that electrician number 2 a year down the line may choose to use that duct for another cable, so he digs it out, make a space, then repacks and seals.

 

The capping material really is nothing fancy, it is usually fire resistant to stop fire spread. 

 

https://www.dortechdirect.co.uk/everbuild-fire-mate-sealant.html?gclid=Cj0KCQiA5NPjBRDDARIsAM9X1GJ6AsjkfVpVcKUwcV-cJrX3x2VD0xjsQ1Oxp7NbsOykwRzg8jFjre4aAvr3EALw_wcB

[PeterW]

@Diablo Not sure what your reference to micro piling around the underground service pipes means ..? 

 

A boiler weighs no more than 180kg full load - if you used a standard council slab, that’s a 3x2 2” plain concrete slab - bedded on a weak sand and cement mix then it would be fine. You wouldn’t need to dig out more than 4-6” at most. 

 

No need for huge groundworks with an external boiler - keep it simple ..! 

[Diablo]

Gents,

 

I think I can locate the boiler next to the house and avoid an underground run of pipes and power. I will use PeterW's suggestion and place it on a 3x2 slab.. . I can run the pipes though the old flue hole and seal it in the way Carrerahill suggests.

 

What an excellent resource this site and its members are! Thank you.