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Humidity and duct choice

I wandered out to Texas this weekend. Crawled into the Attic Space at my Daughters house to fix a broken 12" duct. Thats not why I went to Texas, but Hell, I'm not going to go by without finding something to fix or improve.
Anyhow, I noticed all the wye branches and plenums were made of Duct board. Leaking at all the tape seems, I got some foil tape and started to close them all up.
My question is, Duck board used because its cheaper or it doesn't wear like metal in high humid environments?
I'm going to go back when things cool down and replace all the ducts this fall. I want to use metal wyes and metal plenums, but I wonder if condensation could cause mold. I assume if I wrap it all air tight with insulation that should work just fine.
Any opinions or experiences in the matter?


  • Jamie HallJamie Hall Member Posts: 12,724
    Sounds like me. I go visit my son and wind up fixing something. Never fails.

    I have an opinion, but very little experience. And the opinion is that if the relative humidity in the duct work is reasonable (yeah, I know -- if this is the Houston area, reasonable doesn't apply) then it shouldn't matter what material the ducts are made of so far as what happens inside the ducts. So I would probably use metal. But -- I would also probably insulate it pretty thoroughly, both to prevent condensation on the outside -- which would tend to rust it eventually -- and reduce the potential for mold on the outside. And to save money... In fact, I would insulate whatever I used for the last two reasons (mold and money).
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • aircooled81aircooled81 Member Posts: 194
    Makes sense, insulation saves Green in many ways!
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