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Thread: Water in flex

  1. #1
    Join Date
    Feb 2009
    Location
    Fox Lake IL
    Posts
    450

    Water in flex

    Just wont to know what you all think and what I sould look in to before doing the job.
    I have a customer that called and said his ac is leaking(unit has not been on this year) This unit is in the attic ac only. main runs are metel duct rans and covered with duct rap. runs are flex most around 5 feet some 10 feet. I found that the flex insulation is full of water and dripping on ceiling. as the unit has not been on its not from ac unit. the home owner close the suppley vent in the winter.the returns stay open. the atic has three atic fans and seems to be vented good.atic fans run on temp only as this is in chicago and very cold this winter. the house is heated by bassboard heat. Iam thinking that the vents are getting warm in winter and the cold attic is making condition that is dripping.
    Has any one come across this and what was going on.
    Yes Iam recomending new flex do to water/mold just dont wont new flex to get wet and leak

  2. #2
    Join Date
    Oct 2005
    Location
    sacramento calif.
    Posts
    1,191
    i call it the spaghetti factor, where warm moist air rises into a gas pack on roof or a furnace in an unconditioned attic colder temps then condense the moisture. running the fan will dry it out , a thermostat with the ability to program short run times should solve the problem. i would look the unit over for water damage as well.
    i was born under a wandrin star.

  3. #3
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    yep, we had a couple hi velocity units do this, we cut a block off piece for the return(foam insulation slid in filter rack) and he closes all the supply diffusers in the fall, pulls the insulation and opens back up in the spring. We also blew in a lot more cellulose on top of the trunk and flexes at that time also so not sure if the added insulation solved it, or the block off plate in the return. One of the 2 solved the issues. But yes the warm room air migrating to the attic was the main issue I am sure of that.
    You can't fix stupid

  4. #4
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,242
    But yes the warm room air migrating to the attic was the main issue I am sure of that.

    House leakage contributes, but those 3 power vents with unsealed ductwork would be where I would first look.
    when ducts are not sealed at the plenum they leak, when attic fans come on they create a negative pressure in the attic making duct leakage worse.
    we can't bury our flex in insulation (hot humid climate) or it condensates. not a cold climate expert by any means..just adding my .02!
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  5. #5
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    3,320
    this reminds me of something that came up during code renewal class... is the customer using propane or kerosene heaters in the house? 100% efficiency has it's drawbacks... namely high condensation in cold ducts... just a thought.

  6. #6
    Join Date
    Mar 2009
    Posts
    12
    I am also in Chicago and can tell you this is not uncommon. It seems that it is most likely warm air migration with condensation pooling in the flex. Replace as much flex with metal (cook county hates flex in residential apps) and a simple preventative that many of my customers have used is to take the filter out of the filter grille an cut in a piece if cardboard or 1/2 styrene foam insulation to block airflow in the winter months.

  7. #7
    Join Date
    Feb 2009
    Location
    Fox Lake IL
    Posts
    450
    Thanks to all. That was what i was thinking.Just wonted to pass this by all of you.again thanks. for the heat its bassboard electric heat. This is in mchenry county and flex can be used.

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