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Condensation Around Forced Air Furnace Vents (from not using it and burning wood)

Post in 'DIY and General non-hearth advice' started by MarkinNC, Feb 4, 2012.

  1. MarkinNC

    MarkinNC Minister of Fire

    Oct 3, 2010
    Leicester, NC
    My wife noticed we have what looks like water damage/stains around a couple of furnace vents in the ceiling. They are at separate ends of the house. Our furnace is a heat pump and we are not using it in the winter. It is up in our attic so the duct work is up in the attic as well. We are postulating that condensation is occurring in the vents and then dripping down.

    Does anyone have any insight on this? We do run humidifiers in the kids bedrooms at night and in the room the stove is in. I have a cheap humidity gauge and try to keep the humidity around 45%. Thanks in advance!

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  2. Swedishchef

    Swedishchef Minister of Fire

    Jan 17, 2010
    Quebec, Canada
    Hey Mark

    Here's the cause of it: the warm/moist air from your house is going up into the vents and cooling down. This in turn forces it to condense on the inner/outer layer of the duct. It then works it's way down and creates wet spots on the ceiling.

    I had the same thing happen to me 2 years ago. MY air exchanger was not installed but the duct work was. So I stuff the vent with insulation (temp solution) and closed the vents as tight as possible.

    Hope it helps!


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