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  1. #1
    Join Date
    Jul 2010
    Location
    NJ
    Posts
    394

    Proper or improper usage of flex duct

    I have a friend who is doing a major renovation of a commercial space. The contractor has installed flex for all the take-offs. The flex ranges from what looks like 8" diameter up to 16" diameter. The runs of the flex look like between 15 and 20 feet each where roughly half of that is horizontal then there is what looks like 2" fiber cloth straps that hold the duct where it drop 90 degrees down to where the outlets will be. I told him these sharp 90 degree bends are restricting the air flow significantly and he should talk to the contractor. I saw him today and said I bet the conversation went like this: "a friend told me this what do you think, and the reply would be your friend does not know what he is talking about". He said yup he asked both the contractor and the architect and both said I am wrong. So, what do you pro's think, is this acceptable or should he insist that they install galvanized elbows where they make these 90 pinch turns in the flex or some other option. Thanks for your input.

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,737
    In our area, on a commercial job (with a permit), we can not run over 6' of flex on a supply. There is a reason for this..................I'm just saying.

  3. #3
    Join Date
    Jul 2010
    Location
    NJ
    Posts
    394
    George2 - thanks. He told me they told him it meets code here (which surprised me), but I am just looking to help him understand if he should have them change this to eliminate the restrictions caused by the pinching of the flex at these tight 90 degree drops.

  4. #4
    Join Date
    Sep 2004
    Location
    Memphis
    Posts
    2,502
    If he had enough slack in the flex he could pull the flex up a little and strap it to make the curve a little less harsh. That would be a very inexpensive improvement. I didn't say its a ideal solution but it'd be better than just leaving it like it is.


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  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,737
    Quote Originally Posted by kirbinster View Post
    George2 - thanks. He told me they told him it meets code here (which surprised me), but I am just looking to help him understand if he should have them change this to eliminate the restrictions caused by the pinching of the flex at these tight 90 degree drops.
    When we run flex to a diffuser, we'll use a 90 degree elbow at the termination point to assure that it'll never knick.

  6. #6
    Join Date
    May 2009
    Location
    Savannah, Ga/H.H. Island, S.C.
    Posts
    1,526
    I use the flex elbow supports. They're called "Flexright".

    This is what your friend needs. See the link below.

    http://flexright.net/

  7. #7
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,051
    The inner radius of the bend should be no less than equal to the diameter of the inner flex.

  8. #8
    Join Date
    Jun 2005
    Location
    mississippi
    Posts
    117
    its 5 feet here. and 90% of the time a hard elbow must be installed on the grill

  9. #9
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    4,123
    If its any consolation, around here flex is real common. I've seen buildings done in all flex, and runs of flex over 25' long.

    I'm not advocating for flex, however. I prefer metal ductwork whenever possible.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,311
    Quote Originally Posted by George2 View Post
    In our area, on a commercial job (with a permit), we can not run over 6' of flex on a supply. There is a reason for this..................I'm just saying.
    Funny thing is. The IMC has no reg against flex duct.
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    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,792
    Quote Originally Posted by kirbinster View Post
    George2 - thanks. He told me they told him it meets code here (which surprised me), but I am just looking to help him understand if he should have them change this to eliminate the restrictions caused by the pinching of the flex at these tight 90 degree drops.

    If an architect and the GC don't care, this is a losing battle.

    Drop it.
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  12. #12
    Join Date
    Jul 2010
    Location
    NJ
    Posts
    394
    Quote Originally Posted by timebuilder View Post
    If an architect and the GC don't care, this is a losing battle.

    Drop it.
    Yes, but the customer is the one that ends up living with the problematic installation not the architect or GC.

  13. #13
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,792
    Quote Originally Posted by kirbinster View Post
    Yes, but the customer is the one that ends up living with the problematic installation not the architect or GC.
    And that is the structure your friend must live and work within.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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