Has anyone here worked with insulated underground PEX pipe for water lines or heating projects?

Hey everyone,

I’m looking into it for a property upgrade and wanted to hear real‑world experiences rather than product pitches.

A few things I’m curious about:

installation challenges you ran into

how it held up over time in different soil or climate conditions

any tips you wish you knew before starting

alternatives you’ve tried and how they compared in your situation

Not trying to promote anything—just hoping to learn from people who’ve actually used it. Always appreciate hearing what worked, what didn’t, and what you’d do differently next time.

What are you trying to do specifically? Indoor and/or outdoor project?

Pex is pretty unstable outdoors, UV rays cause it to degrade. It's mostly used for indoor plumbing. I guess if you were to insulate it, it would protect it but it seems like extra work when you could just use polyethylene pipe in an outdoor setting. Use copper stubbed outside of your house to connect to it, not pex.

I don't know exactly what you're trying to achieve but, generally speaking, use poly pipe outdoors and pex indoors.

I have only worked indoors with it.  It seems to do well.   I have heard that underground it is attractive to mice, etc.

Just run normal pex underground, the insulation does nothing because there's nothing heating it.  Like insulating an unheated shop. (It may protect it from heating cooling cycles/vibrations sanding the pipe through) I'm not sure that's ever even happened but then use a pvc sleeve so you can pull a new pipe through later like they do electric.

Obviously it must be below the frost line. Around here that's 2ft and at that depth rodents aren't a problem. Can't speak for extremely shallow installation

Don't bury any connections.  That's important.

Use (pex a) like uponor if you're extra paranoid

Both below and above ground I like to insulate the hot water line especially on long runs. PEX will shed a lot of heat.

I second Martin's suggestion not to bury any connections.  

Normal procedure is encase the insulation and PEX in an external conduit to protect the assembly.  So mice and external weather are less of a problem.  Being properly buried reduces it even more.

Only one I know of, as a problem was fiberglass wrap installed in PVC conduit around PEX.  Their mistake was aiming both ends up and it gathered moisture so the insulation failed.  So if you use a permeable insulation be sure the pipe is sloped so it can drain and stay dry.  Can't help otherwise.

I’ve installed the boiler style-hot and cold both pre-run through a single corrugated drain tile. It is easy to install…until you need to go into an existing foundation. It doesn’t have much insulation between the hot and cold lines so you bleed a fair bit of heat to the return line but at least it isn’t lost to the dirt.

I have also helped with home-brew fixes when rock prevented burying deep enough for a short stretch.  None of those solutions are anything I would want to do for more than 20 feet or so.

Some people think PEX won't break if it freezes.
But I had some break on top of the ground, and it has broken underground in our town when it froze.

Off topic a bit but I'd run 1/4" PEX next to the line so if it ever did freeze I could hook it up to my car and pump hot antifreeze through it.
It just sucks when the water line freezes. Often have to wait until spring and the ground thaws down to the pipe (mine is at 7 feet) to get water flowing again and to see if it broke.

Snow on the ground will help insulate it. Our pipes freeze under the street, but only if it is covered in a solid layer of ice.

I would not run pex underground by its self. Run it in a conduit. Or upgrade to well pipe well pipe comes in 3:4-2” sizes. Keep it well under your frost line.  That’s for water lines if your running it for heat lines use the pex that is in a pre installed conduit. If you’re running that watch out when you cut the bands off. It’s like a spring. It’s a bit hard to run it wants to stay coiled up. For that on the bends put a large log rock or something that won’t break and push / jump on the pipe while someone holds the end it will crack and then lay flat. With this I would also run under your frost line. I’m in the north I have run lots of pipes for yard hydrants for water and pipes to outdoor wood stoves. Pex directly underground is good for about 21/2-31/2 years before a problem comes up. Problem’s never happened when it’s convenient.

I have no experience burying it, but mice chewed through warm water PEX under my kitchen sink so that the length of it they can get to is now wrapped in copper. I'd certainly worry about that happening out in the wild.