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Fostapex for a steam return?

bruce_21 Member Posts: 241
Can I use Fostapex (pex-Al-pex) pipe for a return from a castiron baseboard in a steam system?


  • kcopp
    kcopp Member Posts: 4,383

    No... copper yes. Pex will melt.
  • MTC
    MTC Member Posts: 217
    I'm not sure

    if there's any code allowance for it, but Pex is rated for at least 180 degrees, and that's usually at 80PSI or so. Uponor heating pex is rated for 200 degrees.

    Condensate return is usually around 165 degrees. BUT, this assumes that steam doesn't blow through, which could create big problems.

    I would imagine that you could, in theory, use pex for the wet portion of a return. IF you were to try this, I'd get down well below the boiler water level before switching to pex, to be sure that no steam ever gets to it.

    But none of that is meant to advise using pex, just theorizing...
  • JeffM
    JeffM Member Posts: 182
    not ideal

    I wouldn't use pex-al-pex for anything on a steam system. It is rated to 180 or 200 deg F but as others have said if you ever got steam into the line there could be trouble. Also it is more rigid than plain PEX, but between expansion and flexibility it would be tough to keep the line pitched just right for drainage.
  • pipeking
    pipeking Member Posts: 252
    I have done

    an experiment one time on a steam system i was managing. this system needed stainless in most all of its piping. well, i tried using threaded scd 80 pvc on return piping of a heat ex (near load piping, not past the trap) with a dangerous outcome. i would have never done it if i wasn't able to be close by to watch it. i used a de-rating factor table and thought it could be possible. the temp rating was exceeding the limitations on the pipe so i thought by having very low pressure would compensate, it didn't. 1/2" scd 80 pvc is good for 850psi @73*f and  187psi @ 140*f, those r pretty good numbers for pvc, but once u exceed the max temp it drastically decreased its capability. word for thought!
  • SWEI
    SWEI Member Posts: 7,356

    is not really suited to high temperatures.  Polypropylene is a better choice, but I don't think I'd connect it to a radiator.
  • Rod
    Rod Posts: 2,067
    Plastic Steam Pipes

    Hi- The only plastic pipe I know of that can be used for steam is polysulfone. However since it is a "specialty" pipe, it probably isn't commonly available in the size you would need. I'd stick to copper or black pipe. As others have mentioned, using plastic pipe would likley give you  pitch problems.

    - Rod
  • jumper
    jumper Member Posts: 2,206
    rubber or urethane ?

    There are floppy tubes that can take the temperature. Just look under the hood of your truck. It's even called radiator hose, ha ha ha. Find rejected aircraft tubing, hydraulic, coolant, whatever; I bet it will last in low pressure steam environment longer than any of us will be around. I don't know if it's still sold, but I remember premium automotive rad hose guaranteed to outlast your car.
This discussion has been closed.