Attic ductwork condensation
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  1. #1
    Join Date
    Aug 2012
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    R.i.
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    3

    Attic ductwork condensation

    Register boxes are uninsulated in my attic. What is now being used for register boxes that will prevent condensation and mold ?

  2. #2
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,478
    They should be insulated with duct wrap all the way to the ceiling.

  3. #3
    Join Date
    Aug 2012
    Location
    R.i.
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    3
    What thickness of insulation ? Boxes are sheet metal , are there new materials being used for attic a/c supply and return boxes ?

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,579
    Thread moved to AOP Residential forum.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,829
    Boxes should be insulated that same as the rest of the duct. They're just as subject to sweating as any other duct in an attic. The boxes should also be sealed to the sheetrock ceiling to prevent water stains from forming around the diffuser.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,118
    R-8 ductwrap is the highest R-value insulation.

    short of changing the boxes to internally insulated boxes,
    wrapping them in ductwrap is the only other option
    that I'm aware of.

    as stated above ductwrap should be installed all the way
    to ceiling. ductwrap around box, not compressed and
    then on the other end of the supply box,where duct connects, the
    ductwrap should be installed over mastic seal of joints
    of connection to supply duct. (yours are sheetmetal ducts?)
    ductwrap stapled with duct wrap stapler and seam covered
    with fsk tape.

    make sure hvac company understands not to put new
    duct wrap over old duct wrap. two vapor barriers
    will cause condensation within the insulation.

    sheet metal ducts have long seams, joints where 90 degree ell's
    are installed. these should be sealed with mastic as much as
    possible. then at supply plenum where ducts connect should
    also be mastic sealed.

    where plenums both supply and return connect to heating
    equipment should also be mastic sealed.


    Return air should be mastic sealed.

    then from inside the house, mastic seal supply boxes to sheetrock
    ceiling. attached is photo of mastic sealed supply box

    have hvac company use only mastic to seal these areas.
    both paint on mastic in a gallon bucket applied with a brush
    and mastic tape (not duct tape..not foil tape.. mastic tape)
    can be used.

    bucket mastic should be UL 181 rated.
    I perfer hardcast brand #1402 mastic tape above
    all other brands.

    insulating without air sealing does not stop
    condensation.

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

  7. #7
    Join Date
    Aug 2012
    Location
    R.i.
    Posts
    3
    Thank you for this thorough and greatly appreciated comment on how to do this correctly .

  8. #8
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,118
    not a problem.
    share the information with others.

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

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