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How to prevent plumbing vent from freezing?

0 votes


    Judith says:
    September 25, 2011 at 11:17 am
    We live in Northern MN and our vent pipes were also freezing in the winter. We have a newer home and the vent pipes were slightly below the roof line. We painted the vent pipe black, that did not solve the problem so we extended the vent pipe above the roof line.
The vent pipes still froze-we have 2 vents. We went to L&M and found a black plastic boot type thing that fits over the vent pipe. It is black and the middle of this boot rests at the top of the vent pipe.
    This boot, directly above the top of the vent pipe, has about three holes and there is an insulating Styrofoam inside the bottom half of this boot. The part of the plastic boot that is above the vent pipe is aprox 10 inches long and the part below the top of the vent pipe is aprox 10 inches long. This seems to help but we have to watch so the snow does not pile up and cover these three wholes on the top half of the boot.
    A plumber also suggested we check the insulation around the vent pipe within the attic area. We have a lot of insulation so this could not be the problem. The vents are PVC and bout 4 inches in diameter.
    I don’t understand how these pipes could freeze, prior to the use of the boot, do you have any ideas?
    Thank you
asked in Plumbing by darekrudy (21,730 points)
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1 Answer

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Hi Judith,
        Plumbing vent pipes freeze up during the cold season / in low ambient temperature because sewer gasses are much warmer and as soon as they reach the exposed (cold) section of the pipe they condensate on interior walls. Condensation starts freezing and building up inside the open pipe, eventually sealing the entire vent.
        Insulating the exposed section of the PVC vent stack (as well as unheated attic part of the pipe) is probably the best idea. I’ve seen people using heat tape on PVC but that might melt the plastic and even burn the house down. Is the insulating boot you’ve found in the store designed for the vent stack (do you know its manufacturer by any chance?).
answered by darekrudy (21,730 points)