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  1. #1

    12" flex duct failure

    Howdy, i was just curious: I had a 12" flex duct being used as a return, the inner membrain core colapsed after less than a year of service. Is this a common occurance? or a manufactured fault?

  2. #2
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,259
    Doe's it have a metal helical coil in it? What are the materials of this "flex duct".
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  3. #3
    Join Date
    Jan 2005
    Location
    Emerald Coast
    Posts
    933
    .
    My best guess is an installation error.
    .
    Do not attempt vast projects with
    half vast experience and ideas.
    ...

  4. #4

    Angry flex duct failure

    Yes, to the first response, it is a master flow 12" flex dust R-8 insullation. i would guess a home depot special, but it only has been used just under a year. To the second response: the installation was a professional install, but prior to the flex, there was rigid. The contractor felt the flex was less expensive, minus the 90"s and fittings for moving the duct through the space. as a homeowner, the air return must have been a custom install from the begining. home built in 75. the return is 2, 24"x24"x6" boxes with 12" collar out the side. i have always placed a 20x20x1 inch filter in those boxes. (never had failure) until we switch the returns from rigid to flex. (no size changes)

  5. #5
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    without knowing the specifics of your system it's quite possible that a 12" R/A is too small and it didn't just fail, but was sucked apart by the system.

  6. #6

    Smile Thanks for the help

    Before i contact the prior heating company that did the work, i will have the system reviewed by an outside company. Thankyou for all your help. Any other idea's are always appreciated.

  7. #7
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190

    The filters in the return boxes

    put the flex duct under a good negative pressure

    When you added to the negative from the airflow from a duct size that should have been increased to 14in when you changed from hard to flex
    Then you put the flex under a higher than expected negative and it collapsed
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  8. #8
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,161
    Genduct..that was what I thought too.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    It's pretty obvious that the new flex duct was under a significant suction from the blower. Any repairs should be done after a load analysis to determine the actual size the equipment should be for the home. If there's no surprises from that analysis, then you can determine the size the return air needs to be to keep the suction or static pressure within reason. I normally don't want to see a return air static over .2 IWC nor a supply static over .3 IWC for a total of .5 IWC total ESP. At .2 IWC you would have no trouble keeping a flex duct round.

  10. #10
    Join Date
    Jun 2011
    Location
    Houston area
    Posts
    1,493
    Quote Originally Posted by genduct View Post
    put the flex duct under a good negative pressure

    When you added to the negative from the airflow from a duct size that should have been increased to 14in when you changed from hard to flexThen you put the flex under a higher than expected negative and it collapsed
    Bingo.

    About 5 years ago I was introduced to a new "green" flex that was not supposed to collapse under any conditions, even if stepped on. But that doesn't mean the return shouldn't have been the correct size to begin with.
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

    `. .` .>(((>

    `... `. .` .>(((>

    .` .>(((>

    LMAOSHMSFOAIDMT

  11. #11

    Smile By the way,

    Beyond the flex duct, We have a Day/knight 383KAV Lp i was told the furnace is to big, The home is 1500sqft. It has been operational flawless for 1995. 100,000 btu? We are looking at adding a heat pump Lennox 14HPX042 to reduce the usage of LP. Without high efficient windows we chew through 300 gal fuel in 2 or 3 months. so, you can see, we need to cut the fuel, hopefully without replacing our old reliable. P.S. if the return does not permit to increase to 14" flex, we may go back to 12" rigid. Anyway there is some food for conversation, also does that model of heat pump sound like a good choice of manufacture, and service ability..?

  12. #12
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,350
    12" flex on a 3 1/2 ton system? OH MY!
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  13. #13
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,350
    Mite what to have someone check your heat exchanger.
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

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