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  1. #1
    Join Date
    Mar 2009
    Posts
    5

    Mixing Rigid and Flex ductwork

    My current ductwork consists of a main trunk for supply that is rigid, with flex off of it (ranging from 4 to 6") to the supply registers. All of the returns are flex.

    I have read on these pages that each usually has a different optimal air velcoity.

    Since I am redoing my main trunk as part of finishing the basement should I just go ahead an get rigid ductwork throughout? So far the bids have included reusing the flex and just reworking the main trunk to get some more headroom.

    I dont want to go cheap on reuse of flex if mixing them is a bad idea.

  2. #2
    Join Date
    Jan 2009
    Location
    Indiana
    Posts
    3,228
    commercial work mixes them on a regular bases...ridged off the unit then flex to the diffusers reduces the vibration from the unit. But again that is commercial..i am not sure how home codes are

  3. #3
    Join Date
    Sep 2005
    Location
    Bay Area, CA
    Posts
    843
    City codes will vary on what you can and cant do, but as long as ducts are sized properly there would be no issue.
    Global Warming or: None like it hot
    No pleasure, no rapture, no exquisite sin greater... than central air. -Dogma

  4. #4
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,547
    We mix them quite frequently. No biggie. Check codes in your area. Keep in mind that going rigid is going to significantly increase the costs associated due to increase in price of materials and the labor to do it.
    I like DIY'ers. They pay better to fix.

  5. #5
    Join Date
    May 2002
    Location
    MEDIA PA
    Posts
    1,381

    Is

    the unit in an attic or basement ?

  6. #6
    Join Date
    Mar 2009
    Posts
    5
    Quote Originally Posted by Big View Post
    the unit in an attic or basement ?
    It is in an unfinished basement which is in the process of being finished.

  7. #7
    Join Date
    Apr 2008
    Location
    Galion, Ohio
    Posts
    83

    flex duct

    Flex duct is ok in certain application. If it is not stretched all the way it reduces the CFM.

    But nice for attics or crawlspaces....or a floor joist with a finished ceiling on the other side....

    Its insulated too.....We use it for attics, crawls, tight places where we absolutely cant get ridgid pipe installed.

    IMO If you had good airflow before, it would be ok to leave it

    Plus as bmathews said....consider pricing...a box of 25ft flex is cheap!

  8. #8
    Join Date
    Apr 2007
    Location
    Marion, IL
    Posts
    59
    flex duct should never be used in a crawlspace

  9. #9
    Join Date
    Apr 2008
    Location
    Galion, Ohio
    Posts
    83

    okay

    In many crawl spaces, at least with some of my experiences, the customer is just glad that they are able for us to get duct from point a to b. not to mention insulating the duct.


    Not questioning you at all, just saying....sometimes in shallow crawls, we run flexible duct...

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