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  1. #1
    Join Date
    Jul 2012
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    Re-insulate existing duct insulation?

    First post to this site. I am having an issue with duct insulation condensation which is not uncommon in Florida along the coastal areas. The ductwork is sheetmetal with R5 ductwrap about 24 years old. The sheetmetal portion is still in excellent condition with no leaks (per Florida Power and Light duct load test). Ductwork is located in the attic. The vapor barrier is showing aging signs where the scrim coat is oxidizing and breaking down but all in all the over all ductwork looks to be in very good condition. My question is this: Anyone ever apply a second layer of insulation where the first layer (old insulation) will have numerous holes to be poked through the vapor barrier first to in essence eliminate the old vapor barrier. Then apply the new or second layer of duct wrap insulation? Your input would greatly appreciated.

    John H

  2. #2
    Join Date
    May 2004
    south louisiana
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    personally I'd unwrap old wrap, mastic seal the ducts, add sheet metal
    screws to hold scetions together and re-wrap with R-8 ductwrap.

    old ductwrap is usually R-2 for over 25 years old
    R-4.2 for under 25 years old.

    to double the efficiency of the ductwrap is a no brainer.
    as is sealing the ductleakage. hard pipe leaks like a sieve.
    as the old ductwrap is taken off, the dirt trails on the fiberglass
    corresponds with the leakage sites. long seams, junctions, seams
    in 90's..all these areas leak.
    a bucket of mastic..a box of sheetmetal screws would make
    a lot of difference.
    did florida power test for duct leakage?

    in my hot humid put a second vapor barrier
    over the existing although deteriorating vapor barrier will cause
    condensation between the two. wet insulation = zero insulation.

    having inspected double layers of ductwrap on jobs & observed the moisture
    and having unwrapped, screwed and mastic sealed then re-insulated
    with R-8 ductwrap makes it a no brainer for me.

    now there are lots of arugments about exactly where the condensation
    forms within that double vapor barrier..but to me..its a moot point.
    that it forms at all is the issue.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  3. #3
    Join Date
    Jul 2012
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    Thread Starter
    Hi Energy_Rater_La,
    Appreciate you taking time to respond. The R value is 5.0. We installed the ductwrap ourselves back 24 years ago. Owens Corning. At that time we went with the higher R value available. As for duct leakage. There is no duct leakage. Florida Power and Light did a full duct load testing and the technichian who performed the test is an old friend that I used to work with at FPL many years back. His comment was that as far as leaks go there are none. The reason for wanting to pursue re-insulating over existing duct wrap is due to no duct leaks and essentially good insulation. Was thinking of perforating the current existing ductwrap vapor barrier so in essence the current vapor barrier would be destroyed with the perforations. Then apply the second layer for increasing the R value. I have pulled back a couple of sections to inspect the original and it looked good with the exception of vapor barrier starting to deterioate.

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