Metal vs fiberboard trunk lines
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  1. #1
    Join Date
    Dec 2005
    Posts
    2
    Which is better for trunk lines - Metal or Fiberboard (I think that's the right name)? I'm building a 1 1/2 story home and the HVAC contractor says that fiberboard is best in the attic for the upstairs unit because metal trunks will absorb heat (I live in Alabama) and cause the system to lose effeciency. He says metal trucks in the basement for the lower unit.

    Is he feeding me a load of bull?

    Thanks for your help!!


  2. #2
    Join Date
    Apr 2004
    Posts
    7,680
    Well, ductboard is basicly insulated. If he runs metal duct in the attic or knee walls he would have to insulate them. I personally dont see a problem with ductboard if it's installed right and you keep up with maintnence.

  3. #3
    Join Date
    Apr 2003
    Location
    California
    Posts
    634
    duct board should save you some money
    and its just as good..

  4. #4

    Metal vs fiberboard trunk lines

    not a pro, but a homeowner here with bad experience. just paid big $ to replace a 20year old Trane system AND all fiberboard trunk.

    we have washable filters we clean monthly and i clean the coils once a year.
    but the fiberboard was coated with mold throughout the trunk especially where it joined the air handler.
    trunk and air handler were in the crawlspace though, where there was lots of condensation dripping off the ductboard.
    the insulation in my air handler was always soaked and never dried out in summer. even though the unit was level, excess water sat in the flat rusty drain pan. much of that moisture circulated and the fiberboard soaked it up. i was there when my installer pulled it out and he didn't want to go near it. no wonder we always seemed sick.

    we left the ductboard return boxes because they weren't too bad. was able to vacuum them okay.

    my feeling is ductboard/fiberboard is probably okay with new air handlers that stay dry (esp. those that have sloped drain pans).

    i didn't want to take any chances though. my new trunk duct is all round metal wrapped with R6 insulation. easier to clean and probably better airflow.

    hope that helps your decision.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    The water was likely coming from the coil or drain pan,due to an undersized return duct system(static to high).

    Here in Florida ductboard is everywhere,mold isn't.

    Designed correctly,ductboard or metal,the air flow will be the same.

  6. #6
    Join Date
    Oct 2005
    Location
    Omaha, NE
    Posts
    309

    My suggestion to frieswiththat

    is:

    1. Have your home tested for mold, which can cause significant health problems.

    2. Have a second opinion re your HVAC to see if anything can be fixed.

    cn

  7. #7
    my system and ductwork was already replaced in October with an American Standard variable system & metal ductwork. new system is working like a champ except compressor starts up noisy (see my other post).

    i was just relating the condition of my old system/ductwork which had fiberboard with mold growth. i'm sure fiberboard can be installed right. wish i had taken pictures of the old system to post though.

    i never had tests done to the old system, it was too rusted out to be worth it. i wouldn't doubt that my old system was not originally installed properly. clearly the water was not getting out. as a matter of fact, the last straw with that system was the air handler electrical harnesses were so corroded from moisture they shorted out and melted.

    mold is naturally everywhere. just don't want to be breathing it in a confined, concentrated space.

  8. #8
    Join Date
    Sep 2003
    Posts
    1,311
    A system which encourages mold growth is not designed correctly, installed correctly, or properly maintained.

    I would agree with your contractor. I would advise to ensure that an iron-on tape is used since it will not come apart - many problems can be had with self-adhesive tape holding the ductboard together. Also pay a little extra for the "black" ductboard - it's more durable.

  9. #9
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    I am in Alabama - gtndixie

    I never do and never would use ductboard. The only reason a contractor installs this is because it is easier for HIM to do. I would absolutely install round metal trunk line with exterior insulation.
    No matter how good the install, ductboard traps duct and dirt, and mold, if there, a LOT more than round duct.
    I have replaced several ductboard systems for HO's.
    One for black soot blowing out of registers, several for damaged trunk lines. One for branch takeoffs leaking badly, etc. Have never replaced round trunk line other than for resizing. ( That tells me alot right there )
    My recommendation is round trunk lines with outer insulation, and have installer co.use round duct takeoffs ( that come with foam sealant tape already installed) for all branch line connections. Make sure they tape all joints and use screws to join all metal ducting, including takeoffs. And if insulated correctly, no problem in attic.

    Good Luck,
    Richard

    [Edited by bornriding on 12-14-2005 at 07:43 AM]

  10. #10
    Join Date
    Dec 2005
    Posts
    2
    Everyone, thanks for the helpful info. I got some good ammo to use when I talk with my HVAC contractor again.

  11. #11
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    One last thing.....I prefer metal over ductboard as you don't have to worry about fiberglass particles being blown into you house. Ductboard is everywhere here, but I'd spend the little extra for metal. The metal duct can also be cleaned easier in the future if it ever needs it compared to fiberglass. JMO
    If everything was always done "by the book"....the book would never change.

  12. #12
    Im from lower Alabama and think ductboard is fine in any application,and cheaper just dont sit anything on it and make sure he puts mastic on all the joints

  13. #13
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    QUOTE]Originally posted by da ac man
    Im from lower Alabama and think ductboard is fine in any application,and cheaper just dont sit anything on it and make sure he puts mastic on all the joints [/QUOTE]


    I mean no offense, but doesn;t ductboard retain a lot more dust, dirt, and mold problems over the years than metal??
    And is that not a IAQ problem??

    Richard

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