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dryflydryfly
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    JWG wrote:


    Ok, anyone with a new home that has an air exchanger:

    During the winter the intake vent piping for our air exchanger, and even our passive air vent in the extreme cold, causes such bad condensation that the insulation around the venting saturates and drips. For context, the vent pipe is that flex piping with about 2″ of fiberglass insulations around it and covered with that black plastic.

    So, the cold air comes in and the warm house air causes such condensation that the insulation around the vent piping saturates roughly 3 feet into the house and water drips. It’s not a huge deal now because we have an unfinished basement but two issues:

    – That insulation is so wet it will never dry – will probably mold

    – If we were to finish our basement that would be dripping onto a finished ceiling causing damage

    We’ve already had the vent pipe replaced once because it happened last winter (new home we just moved into last year).

    Thoughts on how to resolve? I’ve thought about adding more insulation between those floor joists the vent runs along to keep the warmer basement air off. But I’m getting annoyed.


    You can try more insulation but it has to be wrapped really ‘tight’ – I don’t mean physically tight but sealed off tight so warm moist air in the house doesn’t contact cold surfaces inside the insulation. If the air leaking in comes in contact with any surface colder than the dew point of that air – it condenses. The problem then accelerates because wet insulation doesn’t insulate well – so that cold surface gets colder and the area larger. It only takes a small air leak for this to take off.

    People think adding insulation is a savior – it isn’t necessarily if moist air is infiltrating the insulation and condensing – in some cases even freezing in there if the inner outer temp gradient is large enough.

    BTW this same thing can be going on inside your walls – it’s a major cause of mold in poorly sealed homes.

    You can try more insulation but I think you will need to really wrap it well so moist air doesn’t infiltrate into the insulation. If it does it will find the coolest surfaces and condense out to beat hell.

    The other option is lower the humidity in your home during really cold periods. Maybe a lot lower. If the inner part of insulation closest to the outside air reaches a temperature of say … 40 degrees… you won’t have condensation if the dew point of air inside is home is lower than that. But understand – 70 deg air with a dew point of say 35 degrees is REALLY dry. Wood splitting nosebleed dry. That’s my home almost all winter.

    Love to hear what others experience.