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  1. #1
    Join Date
    May 2006
    Posts
    19

    Question Duct Sealant Life

    How long should the sealant around plenums / ducts last before developing air leaks? By sealant, I mean the white substance that seems almost like plumber's putty, but not as flexible.

    I'm asking because I have a new home with HVAC ductwork that has been installed for about four months and I can now feel small airflow leaks in the ductwork above the plenum. This system supposedly passed a "smoke" test when installed. I'm trying to decide if this is a reasonable "call for a warranty" repair, or if it is normal homeowner maintenance.

  2. #2
    Join Date
    Jul 2003
    Location
    Massachusetts
    Posts
    288
    longer than 4 months

  3. #3
    Join Date
    Apr 2003
    Location
    California
    Posts
    634
    should last a lot longer than 4 months, I have worked on systems that are 15 - 20 years old and have had to fight with the sealant to get it off. call the installing company to check it and redo if need be , should be under waranty.

  4. #4
    Join Date
    May 2006
    Posts
    19
    Thanks.

  5. #5
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,305

    Cool

    Duct sealing mastic will last many years. If you are getting air leaks, there are several things to consider:
    -minor leaks are not a concern: just close the barn doors
    -they may have missed a few spots originally. It may have been leaking all along and still been able to pass a Duct Blaster test.
    -Large gaps usually require mesh tape reinforcing. If you have a large leak, try to determine if it is along a seam or big gap and if there is mesh embedded in the mastic.
    -for transition gaps such as interesting trunks or panned joist ends, foam may be a better choice.

    Note: duct sealing, while great and necessary changes the airflow in and out of the furnace. Once you seal it, you really need an HVAC contractor to come back to check the furnace. He'll need to perform a combustion analysis, measure duct pressures, etc.

    HTH,
    Hearthman

  6. #6
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,375
    The grey stuff is better!

  7. #7
    Join Date
    Nov 2006
    Location
    North Carolina
    Posts
    130
    10 years, Duct leakage will increase energy cost. The unit may work good for years with leaking ducts but when you have several degree days in a row if the unit was originally sized properly you will see the problem. I would get the duct sealed properly if you want the seer rating you paid for.

  8. #8
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    Most states require a 12 month warranty on installed products. (Somebody correct me if i'm wrong) I would call the contractor back who did the sealing and point it out to him/her. If the contractor is a good one, they will fix the problem. Some "pin hole leaks" are normal, such as rivet seams on adjustable round ells. We try to seal everything when we do our installs. We duct blast ALL our installs. There is a permissable amount that can leak, but the tighter the duct, the better the energy savings. We have installs on 2700-3200 sq ft homes that test out at 9-30 cfm ( before equipment ). We have found that most of the leaks are discovered at the air handling equipment. I agree with arc 8 the gey stuff is better! Sometimes the oil on the surface of the sheet metal will not let the mastic stick very well.
    Genius = The guy who can do anything...except make a living!

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