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Community and Q&A

Condensation in Unheated Porch

dogmop | Posted in General Questions on

When we installed A/C, we decided to cool an unheated 3-season porch.  We live in New England. The A/C is in the attic as we did not have forced air system and use oil for heating. We were advised to shut all the vents once we start to use heat so that the warm air would not escape into the A/C vents.  We had a very cool day and suddenly it got warm (this happened in the winter months), weird weather, and we got condensation only on our unheated porch where the two vents are located. Nothing in the house.  We were told it was caused by condensation.  Should the vents on our unheated porch be left shut or open in the winter during cold temperatures?  One person said open, the other said closed.  Thank you.

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  1. Expert Member
    BILL WICHERS | | #1

    Chances are warm, most air went up through the vents in your living space, condensed on the inside of the cold, metal ducts, then ran out as liquid water through the vent where you're seeing the problem. You would want all the vents shut, but they probably also all leak (those integrated dampers are far from air tight), so you'll still have air leaking up there. When conditions are right, even that small amount of leaking air can cause problems.

    What I have done in the past to deal with this type of issue is to use painter's tape to tape some heavy paper over the vent as an air barrier. This is easy to do, cheap, and doesn't require any major rework. I'd try that and see if it solves your problem.


    1. dogmop | | #2

      Thank you. That helps.

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