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Thread: Ice on plumbing stack

  1. #1
    DIY Junior Member jdsweeney's Avatar
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    Default Ice on plumbing stack

    Hi there,
    I've recently had a problem with ice building up on my plumbing stack. I've tried to do some research on my own and haven't found any information pertaining to my specific problem. I discovered the problem the other morning while working in my basement. I've had an ongoing basement renovation and noticed that there was a small pool of water on the floor directly below one of the drains for the main floor. I took a look at the drain and noticed water built up around one of the fittings so assumed that somehow the fitting wasn't glued properly. I kept an eye on it the rest of the day and was surprised to see that the leak didn't continue. The next morning i got up and checked it again and noticed that there was ice frozen to the bottom of the drain, we've had a stretch of -30 C temperatures and my basement was partially uninsulated and had only one small heater in it. I assumed that this was caused by condensation from the cold basement and the warm upper level so I finished insulating and installed another space heater to make sure that the basement never dropped below +7 C but again the same problem with water again. I've cut out the drywall around the stack on the main floor and found more ice build up on the outside, it isn't an exterior wall and the air around the vent can't be cold enough to freeze water. Anyways, I thought I'd give you all the info to date to better understand my next question. Recently, I had plumbers rough in a wet bar and laundry room. i didn't have the necessary slope to install a drain below grade so I had to use a grey water pump. The pump wouldn't work properly with cheater vents so they had to run a new vent for the pump, laundry, and bar area out the exterior and up the side of the house. Is it possible that by doing this the plumber changed the pressure so that now the main stack is constantly sucking in cold air from outside causing condensation to form then freeze on the outside of the vent overnight and ultimately melt the next morning when we start running the hot water?
    Any insight would be much appreciated, thank you
    Joel in northern Ontario

  2. #2
    In the Trades Tom Sawyer's Avatar
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    All stacks are suceptable to frost closure which is why in northern states the minimum diameter of the stack as it penetrates the roof is 4" and that 4" has to extend 18" below the roof line as well.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    DIY Junior Member jdsweeney's Avatar
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    Default

    Thanks for the reply,
    The stack is 4" in diameter and does extend 18" below the roof line. I don't think this is a frost enclosure issue. I have moisture accumulating and freezing to the outside of the stack even inside of my warm envelope. Something has changed due to the work that's been done in the basement and the only thing that I can think that would have affected my venting system is the new vent for the pump. I'm trying to finish the basement and can't drywall until this moisture issue is solved. Any other suggestions?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Hot air rises...if you have the vent open while remodeling, it will act like a chimney, taking the hotter/moister air up and at those temps, it will condense - whether it flows back down or freezes, depends on where it happens. If you've added a trap, and the trap is not filled with water (say, you haven't hooked up the sink and faucets yet), pour some water in there to create the seal. If you've already done that, let us know, and maybe we can think of some other things.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Member BillTheEngineer's Avatar
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    If you seal around the vent pipe where it enter the attic (I assume you attic is unconditioned space), it should eliminate the frost from forming on the outside of the vent pipe. You should seal any opening between the conditioned and unconditioned spaces. The opening allow for a draft, just from the differences in temperature between them. The same holds true for a basement if its an unconditioned space. But in a basement normally you would seal between the outside and the basement, but sealing between living spaces and basement also helps to eliminate drafts.

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