underground pex insulation

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I am planning to use 2 inch insalation board to create a box that is 6 x6. I am running 2 1" 1/4 and 2 1'"pipe. I am going to seperated the pipe with 1" insulation and then spray tiger foam inside. My run is 50 feet. I I am using the insulation board to save mony on the foam spray. Do you see any problems with this.
thanks joe

 

[bpirger]

When I first put in my system, I burried 1" he-pex, wrapped in insulation, inside a 4" conduit (two lines actuall). I surrounded this 4" conduit with 2" of extruded polysytrene. I'm replacing that now with microflex as I install a Garn.

Two observations:

1. Without a doubt, I would melt some snow on top of this conduit, which was only about 3' deep here in NY state.
2. I just dug up a section of this, and I was really surprised to feel how heavy the polysytene insulation was. It was waterlogged...and I suspect it wasn't helping much!

So my experience has been that burried pink board gets wet. Now this is out in the open where the rain falls....Hopefully the insulation under my concrete is dry!

 

[ewdudley]

When I first put in my system, I burried 1" he-pex, wrapped in insulation, inside a 4" conduit (two lines actuall). I surrounded this 4" conduit with 2" of extruded polysytrene. I'm replacing that now with microflex as I install a Garn.

Two observations:

1. Without a doubt, I would melt some snow on top of this conduit, which was only about 3' deep here in NY state.
2. I just dug up a section of this, and I was really surprised to feel how heavy the polysytene insulation was. It was waterlogged...and I suspect it wasn't helping much!

So my experience has been that burried pink board gets wet. Now this is out in the open where the rain falls....Hopefully the insulation under my concrete is dry!

My experience with pink board in the same climate was similar.

We had a couple shallow lines that went a few feet out to couple cistern tanks, which I insulated from freezing with polystyrene board. I used two layers of some scrap pieces of one inch board, both pink and blue, and had them well covered with a couple layers of 4-mil plastic sheeting, then another layer of one inch board, then six inches or so of fine gravel on the surface.

It worked for freeze protection, but when I dug the mess up after six years in order to add a mechanical room to the house in that area I found that the plastic sheeting was (duh) a vapor barrier and there was apparently constant condensation below it, so that the board was wet all the time.

At any rate, the blue board was crisp, dry, and light, while the pink board was spongy, soggy, and dense. Both were extruded polystyrene, but the pink stuff sure didn't compare well. I've since experimented with boiling both brands to test for suitability for another toy project and the pink performed poorly in hot water as well.

Both the pink and blue were typical big box/lumber yard polystyrene.

I can't imagine what the stuff costs, but if I was going to bury hot water pipes I'd want to see if the high-density 75 psi blue board was affordable.

--ewd

 

[DaveBP]

Not all extruded polystyrene is rated for underground service. Blue or pink. And I've never seen anything printed on the product itself that says so. You have to look it up from the little numbers on the sheet itself.

And I have only run into one building supply guy that knew it and said so when I told him what I was doing. That was years ago. My guess is that the cheaper product is NOT the waterproof stuff. I've dug up soggy polyurethane foam roof insulation board, too.