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  1. #14
    Join Date
    Nov 2003


    I installed real duct in the house I built for myself.
    Flex has it's place...just not in my place.

  2. #15
    Join Date
    Feb 2005
    Dothan, Al
    I never use flex duct as my trunk line.
    Will run flex to branch outlets, no problem
    If my flex run would be longer than 15 ft, would probably run some 'oversized' hard pipe and then reduce down to flex close to boot.
    Flex only used in attic also.
    All hard pipe, under house.
    And I personally don't like ductboard so I don't use it.

  3. #16
    Join Date
    Dec 2003
    As already stated flex was originally designed for connection from a metal trunk to a diffuser a few feet away. It does create more of a pressure loss than metal duct so that must be taken into account when sizing. I too am of the less flex the better persuasion.
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  4. #17


    I'm an old tin knocker myself but I realize flex has it's place and is here to stay so what is one to say?

  5. #18
    Join Date
    Feb 2004
    chicago suburbs
    i like flex........just in small doses.

  6. #19
    Join Date
    May 2004
    Rapid City, SD
    I like flex too... Cut a piece a few feet long, loop it so one end is pushed inside the other (so it makes a tight circle with no hole in the middle), paint it orange and ya got a pumkin!

    I think flex has it's place, but the only place I actually like to use it is on the comercial jobs to hook up the diffusers to the duct, or in some cases in residental where hard piping from the duct to the register would be impossible with out a lot of elbows.

    Personally if I have the choice, I never put flex where it can't be reached once the house is done (between floors or other similar places). In attics, I might use a few feet, crawlspaces only if there's absolutely no other way. Our code says 7' max, I try to stick to 3' myself.

  7. #20
    Join Date
    Nov 2004
    SW FL

    Thumbs up Replacement system

    Originally posted by judgetc
    I was told by the installer that all the duct will be the flexible type. What do the experts think????
    Review the Manual D and J design.
    If it does not exist, go onto the next shop.

    Suggest to use adequately sized ( ~1,000 FPM) duct header of ~ 2 feet per ton at fan outlet.
    i.e. 5-ton, 14"x20" about 10 feet long.

    Flex limit of 20 feet on branch runs is good rule-of-thumb'.

    Add Simple E.S.P. TEST as part of your contract:
    Max. 0.2" in header, withhold 25% of total estimate until static pressure can be maintained at < 0.2". 0.3" if using a variable speed air handler.

    [Edited by dan sw fl on 03-16-2005 at 06:54 AM]
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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