is foam in trench the best way?

[Adirondack Handy Man]

Hi guys
is foaming in the lines on top of 6 mil plastic the best it can get for a 250ft (one way) run of 1 1/2 pex. I do not want to do it twice. ive read some great thing here but really would like some feed back from fooks who have done it this way. i just dont care for the retail things available in this size (five wrap aluma foam). thanks in advance

 

[seige101]

Here is an old thread about foaming in a trench. https://www.hearth.com/talk/threads/underground-lines-not-the-place-to-skimp.50506/

 

[rkusek]

I did about 350' (700' total) of a pair of 1 1/2". I didn't use plastic and can't say whether it would be better or worse since it may actually hold moisture next to the foam. The spray guy just raised the pex up between his feet and shot a few inches underneath, then a few inches all around the pex after that. They quoted me "about $500" over the phone and it ended up being $675 but i think it was money well spent. I don't think I could have bought the same amount of insulation in the "froth packs" for what they charged although I would have been more conservative/selective with the spraying had I done it.

 

[Tennman]

Whatever you do use closed cell polyurethane foam insulation. There are several excellent products you can buy like Thermopex or you can spray your own. So assuming you will use polyurethane the only variable in insulation properties is the foam's thickness. Obviously you can blow/cast a thicker insulation barrier doing the trench method. For a run that long energy loss and cost will be you deciding factors. For shorter runs, maybe 50-60' using Thermopex makes sense since the energy loss will be small and just the expense to get a foamer to your site can be pricey. Usually the way this works out is you get quotes for foaming contractors in your area to do the job. After you get those quotes then you can make a decision because foaming in trench quotes are all over the map depending on region and how busy the contractors are in your area. My contractor was very reasonable but for others the cost of Thermopex was actually more attractive. In your case given the long run, foaming in trench will give the best performance (thicker foam), but if you can't get reasonable quotes... well then a Thermopex type product is your best option.

 

[hartkem]

I went round and round in my head on which way to go. In the end I went with 1 1/4 thermopex and Im glad I did. I had to go up under a slab building and it was tight with not much room. I dont know how I would have sprayed it properly where it entered the concrete floor. My main concern was the foam taking on water over a long time. The thermopex has a thick shell of plastic around it but it is a bear to bend. Others have had good results with the foam so I can't say its a bad idea and with your distance its likely to be cheaper. I would be hesitant to use it if you have a lot of ground water.

 

[Sawyer]

I am satisfied with my installation with closed cell foam. Heat loss over 200' is unnoticeable. Sure saved a lot of money and got more insulation surrounding the four pipes than pex in a 4" tube.

 

[salecker]

I am satisfied with my installation with closed cell foam. Heat loss over 200' is unnoticeable. Sure saved a lot of money and got more insulation surrounding the four pipes than pex in a 4" tube.

I did foam in trench 125 ft,i can't measure any temp drop with an infrared gun,i did twin 1" lines each way.I would do it again even though it was very expencive up here.
Thomas

 

[foamit up]

I did my first one 1 1/4 pipes in a 6 inch drain pipe foamed solid. I spray foam. Put plastic in trench also and sprayed 2 inches around drain pipe. It goes 100 ' under ground. No measurable heat loss. I have sprayed many others with just plastic in trench, this keeps dirt out of foam and uses less foam as you can hold plastic up as you spray. I cover all pipes with three inches which is r21 in foam world. I have them both ways for my boilers and did not notice a difference. Foamit up