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Any ideas how to thaw out

MikeJ Member Posts: 103
3" PVC vent pipe that runs though a attic. Besides burning down the house :)
The pvc runs through the attic and the pvc is not insulated.
Could not get on the roof tonight to look in the concentric fitting,
If you look close you can see ice coming up out of the pipe.
https://www.screencast.com/t/0x3z3dl9Rdi yikes


  • Jamie Hall
    Jamie Hall Member Posts: 22,941
    Lovely. Worse, it's a concentric vent unless I'm mistaken -- and the ice is in the inside pipe. If that is true, then the best thing I can think of is to blow hot air up through the outer pipe.

    If it isn't a concentric, you could also try a heat gun (on low -- PVC can't go over about 170) on as much of the pipe as you can get at, starting at the point where it leaves the conditioned space.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,752
    edited December 2017
    I didn't know you could do a vertical concentric vent. What do I know? I'm more an oil guy.
    When possible I would run a seperate vent and intake. Gooseneck the intake. Minimum 12" between them.
  • MikeJ
    MikeJ Member Posts: 103
    its concentric, I don't their is any easy way to thaw it out. May look a picking up a heat gun. Thanks
  • ch4man
    ch4man Member Posts: 296
    disconnect the vent pipe at the furnace and use either an electric leaf blower or a wet vac that you can hook up the hose to the discharge and blow the warm(relatively) room air through it.

    it'll thaw. just be dang sure to hook up the vent pipe back where it belongs when done.
  • MikeJ
    MikeJ Member Posts: 103
    ch4man good idea, may work
    JUGHNE Member Posts: 11,021
    This won't thaw that out but something to consider: One I&O manual for condensing FAF allow reducing the last 18" of vent pipe to prevent freezing. Wouldn't work for the concentric but for separate pipes is an idea. I don't see this in Lochinvar I&O book though.
  • Zman
    Zman Member Posts: 7,549
    There is a pretty good chance the pipe cracked when it froze. Pressure testing it would be a good idea. Would it be easier to replace the pipe?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Having worked on these boilers for nearly 30 years, I can't say I've ever seen this happen. I've seen the metallic screen freeze with hoar frost. We ended up putting an increaser on that vent and replaced the metal screen with a plastic one.

    I'm not a big fan of that particular concentric vent kit in a vertical application, because you can NOT maintain the code required snow clearances due to the shoulder of the wye connecting with the roofing.

    Just when you think you've seen it all.... And Mother Nature is usually involved.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • MikeJ
    MikeJ Member Posts: 103
    It was mainly block at the outlet of the concentric, got into the attic cut the pipe and was able to unblock from the attic The roof was too icy to get up on it.

    There was ice in the bottom of the 3" horizontal pipe, about a inch thick, had about 15 feet horizontal pipe in the attic.
    Use heat gun to thaw it out, then wrapped the pipe with insulation.
    Got a nice heat gun with temperature range form 150 to 1300 degrees, thanks @Jamie Hall for the suggestion.

    After seeing ice sticking out the top my fear was the whole thing was going to be fill with ice, luckily everything turn out good. B)

    @JUGHNE Lennox dealers in town do that a lot reduce the vent pipe size the last 18" . In town you can only do what is in the install manul for the furnace your putting in, otherwise it will not pass code. Must be in the Lennox manual.

    @Mark Eatherton had real light fluffy snow one night, got called out for a block screen. Not a lot of companies around town install screens,
    JUGHNE Member Posts: 11,021
    JFYI; That reduction of the last length of 18" exhaust vent is also allowed in the Frigidaire/Nordyne I&O manuals.
  • MikeJ
    MikeJ Member Posts: 103