# how to insulate underground pex



## .netDude (Nov 26, 2004)

Thinking about putting an indoor wood boiler in the shop and running pex to the plumbing for the gas boiler in the basement of the house. The insulated, dual pipe pex that comes in what looks like drainage pipe filled with some sort of poly insulation is around $13 / ft, so I'm looking for other options. Can I use that 2" solid foam insulation sold in sheets to insulate the pipes? If so, how would I fasten it together in a box to keep the water out? The box would be about 3' underground, below the frost line. I need a couple hundred feet.
Thanks in advance.


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## DaleK (Sep 23, 2004)

You can find it cheaper than that if you look around.
I would check into getting a length of solid big O tile, slitting it down one side, then putting your PEX in it and putting spray foam around the pipes if you want to do it yourself.


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## matt_man (Feb 11, 2006)

When we put in our outdoor wood furnace we ran 75-100 ft(can't remember exactly) from the furnace to the house. We wrapped the pex (it was not insulated) with 8" foamy insulation. It's just like the 2" stuff for wrapping water pipes but fatter. I used to have a spare piece around and would have taken a pic for you but it is gone now of course. Then we had plastic to go over it. The plastic was like a big 8" round plastic bag, and a pain in the butt to put over the insulation but it is a good seal and we don't have to worry about water leaking in and freezing around the pipes. It keeps everything together and water and stuff out. It is buried about 3 feet deep.

I do have a pic of the final product (where it goes upstairs behind the tub to the blower in the attic).










We got all the stuff the same place we bought the furnace from. It was not cheap though. I would find a place that sells wood furnaces (ours is a Central Boiler) and have them quote you how much it would cost.

Rachel


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## SolarGary (Sep 8, 2005)

Hi,
This is the scheme that I used -- about $1.30 a foot:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/trench.htm

Pretty easy to do.
If you don't have a way to do the dado grooves, you could just substitute some strips of 1 inch thick foam board to capture the pipe.

Gary


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## .netDude (Nov 26, 2004)

Thanks for the responses.
If I wanted to use 1" spacers instead of the dado's like in SolarGary's pics, how would I secure the 1" spacers to the bottom piece. I'm thinking a cross section would be 'W' shaped (squared off bottoms of the 'W') to hold the pipes, filled with poly foam, and the foam would secure the top the the assembly.
Solid big 'O' pipe may be a little less labor, but I'll have to check around and see where I can get that to price it. Think an Ace Hardware or Lowes would have it?


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## DaleK (Sep 23, 2004)

Yep any building supply store should have it.


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## fordson major (Jul 12, 2003)

there is a cheaper brand available, not sure of the name or supplier but will bug ross when i see him!! we use the stuff you are talking bout, works well but costly! when you add our time it is cheap though!


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## SolarGary (Sep 8, 2005)

.netDude said:


> Thanks for the responses.
> If I wanted to use 1" spacers instead of the dado's like in SolarGary's pics, how would I secure the 1" spacers to the bottom piece. ...


Hi,
The polyurethane foam in a can (e.g. Great Stuff) makes great glue. Just run a bead along the top and bottom of the 1 inch spacer piece and press the top and bottom pieces to it. You need to either weight it or tie the bundle together with string to keep the foam from expanding too much as it cures. The foam in a can seals, insulates, and glues quite well.

If you get any on your hands, be prepared to wear it for a week 

Gary


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## Cornhusker (Mar 20, 2003)

Just put it 5 ft in the ground, it won't freeze.


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## DaleK (Sep 23, 2004)

Cornhusker said:


> Just put it 5 ft in the ground, it won't freeze.


Not a matter of whether it freezes or not but how much heat you lose. I've seen a boiler where they ran about 100' of uninsulated line to the house, 4' deep. There was a 3' wide unfrozen path over the line all the way, all winter long, where snow wouldn't accumulate even when it was -40 out. Hardly any heat to the house though.


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## fordson major (Jul 12, 2003)

it's also to keep water away, friend had pipe run in sewer pipe then foamed into blocks. pipe shifted and the foam cracked, water was wicking away the heat. stuff we were looking at but could not get in the 1 1/4 inch we needed when we installed 2 weeks ago. http://www.pinnaclesupply.com/products.html


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## ericjeeper (Feb 25, 2006)

whatever you do, make sure the pipe is free of ground water ever getting to the pex.

I wrapped each of my lines with armorflex then wrapped it all with the silver bubble wrap then I wrapped the entire kit and kaboodle with shrink wrap then shoved it all into a 5 inch diameter plastic corrugated field tile.


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## mink (Feb 10, 2005)

what about insulated sewer pipe?...mink
my outside furnace is buried about fifteeen inches deep here in new york where the frost gets about 40 inches deep and yes the ground above mine does stay thawed but the return water just loses about 5 degrees. but my run is only anout 40 feeet and its inside the black flexible seweripe with no insulation at all. my sister has hers inside the insulated sewer pipe with all the joints sealed with silicone tubes . not sure of the cost of those insulated sewer pipes though , they are 4 inch inside and id say about 9 outside with the foam.


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## SolarGary (Sep 8, 2005)

Hi,

I suppose if your ground is quite wet, there could be a concern about some kind of waterproof shell around the insulation. In our case, I put a couple inches of washed gravel under and over the pipe line -- with our soil conditions, it will never see any water, but we do live in a dry area.

Even if you get some water, the method I showed pretty well seals the PEX inside of XPS rigid foam board. The XPS (this is the pink or blue stuff) is basically impervious to water -- thats why its used on the outside of foundations. I would not use the white polystyrene in that it is more pervious to water, much more messy to work with, and has a lower R value.

Even if the insulation develops some small cracks, it won't allow any water to travel along the PEX, and only effects the R value in the immediate area of the crack.

Aside from saving 5 or 10 bucks a ft, one thing I like about the method is that it allows you to increase the R value to whatever you want by just adding more insulation. It looks to me that (in spite of what some manufactures claim) the insulation in the commercial products tends to be about an inch thick (or even less), and this can't be good for much more than R6 even with the very best insulation.

As an aside, I think it is also good to have some insulation between the two PEX pipes, otherwise you get some heat transfer between the supply and return lines, which decreases efficiency and throughput. I've measured the temperatures at both ends of the supply and return lines quite carefully, and I see a little of this even with 1 inch of insulation between the supply and return.

My 2 cents 

Gary


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## BeeFree (Feb 23, 2004)

When ours was put in for our wood furnace, the 2 pex lines were pulled through white plumbing pipe and elbows glued where needed on to the pipe. That way no water can get inside and if there is a problem with a leak in the pex you can attach to one end and pull more pex through so you won't have to dig up the ground. We live in SE Mo so we don't lose hardly any heat from no insulation. If we had lived in a colder area we would probably have put all those pipes in an insulated pipe of some sort.


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## Cornhusker (Mar 20, 2003)

DaleK said:


> Not a matter of whether it freezes or not but how much heat you lose. I've seen a boiler where they ran about 100' of uninsulated line to the house, 4' deep. There was a 3' wide unfrozen path over the line all the way, all winter long, where snow wouldn't accumulate even when it was -40 out. Hardly any heat to the house though.


Oh, I see what you mean now.
They make pipe insulation, it's kinda foamy. We used to use that, then wrap it in fiberglass insulation and cover it with duct tape. (under a trailer house) It worked pretty good and was cheap.
A guy could stuff that whole works in some pvc if you wanted and it'd still be pretty cheap.


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## .netDude (Nov 26, 2004)

SolarGary - what did you use to seal the seams between the foam boards?


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## Jim S. (Apr 22, 2004)

I'd back off from using the CPVC pipe. By golly, every joint in it is a potential leak! Uh, have you ever tried to find a leak underground like that? It'll run along the pipe, especially since there are grooves for it to follow. Do something continuous, like PEX in the foam. Yeah, a bit more expense, but as others have pointed out, it's cheaper on the repair bills 10-20 years from now.

Now folks'll say, yeah but they use CPVC in the ground for water supplies all the time. To which I say, yeah but that's usually COLD water, not hot water that expands and contracts it all the time.

It's up to you, but if it were mine, I'd want a continuous run both ways. I always think about what if it needs fixed later, cuz it'll be ME fixing it!


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## .netDude (Nov 26, 2004)

Yeah, was more considering the foam boards as insulation with pex for the piping, not cpvc.


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## SolarGary (Sep 8, 2005)

.netDude said:


> SolarGary - what did you use to seal the seams between the foam boards?


Hi,
I used the polyurethane foam in a can -- "Great Stuff" is the most common brand. All the hardwares sell it.
Polyurethane is a great adhesive, as I routinely find out after getting some of the foam on my hands 
After you glue the two halves of rigid foam together with the Great Stuff, if you try to separate it, it will often break through the rigid foam rather than at the joint.

---
I used CPVC pipe not to save money, but because I figured it would be easier to work with than coils of PEX. I've used CPVC for years and never had a problem with a single joint, but I agree the potential is there. If you use the rigid foam method I used, then installing the PEX in the grooves while keeping the PEX straight until you get the two halves of the foam tied together is likely a two person job. Using PEX-AL-PEX would probably be easier, as it holds it shape.
With either pipe, be sure to pressure test before backfilling.

Gary


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