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  1. #1
    Join Date
    Mar 2005
    Location
    RALEIGH
    Posts
    39
    I'm in the middle of installing a Trane 3 ton heat pump sytem. There are 15 6 inch supplies in the crawl. I was told to run 2 12 inch flex 25 feet to #2 distribution boxes and run 6 of the 6 inch supplies off of each of the distibution boxes and run the remaining 3 straight off the supply plenum. I'm curious if both the 12 inch flex can carry those 6 runs coming off the distribution boxes. I have already suggested we run 14 to the distribution boxes but I was told 12 inch flex would be fine. I want to know what you would do in this situation??????

  2. #2
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    flex in a crawl........you'll be sorry.
    FILL OUT YOUR PROFILE!!

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,925
    The 12" should handle the 6 6", but I'm with tinner abouot it in the crawl space.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Mar 2005
    Location
    RALEIGH
    Posts
    39
    My company will only allow us to install flex whether it be in an attic or a crawl. What is the problem with flex in a crawl as long as it is properly installed and up to code???

  5. #5
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Originally posted by tinner73
    flex in a crawl........you'll be sorry.
    In Raleigh, flex is the standard everywhere.

    The only time I run into complete "hard duct wrapped" ductwork in crwlers is when the house is 50+ years old...
    How tall are you Private???!!!!

  6. #6
    Join Date
    Mar 2005
    Location
    RALEIGH
    Posts
    39
    Yeah same here thats the only time I run into hard duct. Things must be alot different around the country. This is the only area I have ever worked in so this is all I know.

  7. #7
    Join Date
    Apr 2005
    Location
    Chicago
    Posts
    23
    Run it in hard pipe , that's all I have ever been taught.
    I just got done rippping out 200' of flex in a crawl , half the runs were not getting enough airflow and the other half you could fart harder than they were blowing.
    Of course they were all coming off of the plenum though.
    I am curious to know how the system would work if you ran
    the flex to distribution boxes? Let us know how it turns out!


  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by blu70devil
    I'm in the middle of installing a Trane 3 ton heat pump sytem. There are 15 6 inch supplies in the crawl. I was told to run 2 12 inch flex 25 feet to #2 distribution boxes and run 6 of the 6 inch supplies off of each of the distibution boxes and run the remaining 3 straight off the supply plenum. I'm curious if both the 12 inch flex can carry those 6 runs coming off the distribution boxes. I have already suggested we run 14 to the distribution boxes but I was told 12 inch flex would be fine. I want to know what you would do in this situation??????

    You will liklely need balancing dambers at each takeoff,as it's not likely that every supply would be 6" flex.

    will you be there for start-up??


    The 12" flexes are most likely large enough to handle the systems air flow,I just doubt it will be the correct cfm in each room.

    What the return duct system like??

  9. #9
    Join Date
    Mar 2005
    Location
    Indianapolis, IN
    Posts
    241
    >I'm curious if both the 12 inch flex can carry those 6 runs coming off the distribution boxes.

    Basic math pi x R * R.

    So 12" = 113 sq in
    6" = 28 sq in

    113/28 = 4.

    So you can have up to 4 - 6" runs coming off 12" duct
    Two 12" -> up to 8 - 6" runs.

    >flex in a crawl........you'll be sorry

    You will be happy with customer calls.
    I mean what are the chances it will develop some holes.
    Mice would just leave those alone.

    BrownOne

  10. #10
    Join Date
    Mar 2005
    Location
    RALEIGH
    Posts
    39
    I finished the job today and the airflow seemed to be just fine. We replaced a 3 ton Trane heat pump for another 3 ton Trane heat pump. The customer said that the airflow was actually better than before. Flex may not be the best thing for a crawl space but thats the only option I have at my company and it seems to be the thing to do here in NC. Overall the job looked great and the customer was very happy with our install.In the end you cant ask for much more than that. Thanks for all the input guys.

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