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  1. #1
    Join Date
    Nov 2007
    Location
    San Marino, CA
    Posts
    5

    flex vs metal ducts

    I have an 80 year old house on So. Cal. We've decided to redo our hvac system and got bids to remove the asbestos wrapped ducts throughout and replace with new ducts.
    My question is that one contractor said that he would use mylar flex duct throughout even in the ducts in the walls. That seemed kinda odd to me, when I questioned him about it he said that that is the way all new construction is done nowadays and it works better with todays more efficient systems.
    Can anyone shed some light on this for me? it seems to me that metal ducting would actually be less restrictive and more efficient or is that just an old school thinking? I guess I'm also thinking that if I'm going to be opening the walls, is it ok to put flex ducting back?

  2. #2
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    liar liar......it's easier to install flex. that's the only reason it exists. not better for airflow.
    FILL OUT YOUR PROFILE!!

  3. #3
    Join Date
    Nov 2007
    Location
    panama city beach (aka lower alabama or LA) FL
    Posts
    93

    flex

    the only reason flex is used is that you can teach a monkey to run the stuff,its cheaper,less labor.and its quicker which means he have his guys in and out and on to the next job in a couple of days instead of a week..........the bad part is you dont get the same airflow out of flex as you do with metal usualy resulting in ducts having to be larger

  4. #4
    Join Date
    Oct 2007
    Location
    Southern Ontario
    Posts
    44
    Don't let this 'contractor' do anything. If he's telling you flex is better than metal, what else is he making up? (asbestos removal, repairs...)

  5. #5
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    run!! find someone else, no matter how much less this guy costs it is not worth it you'll have someone else redoing it again
    You can't fix stupid

  6. #6
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    We are in Florida ,flex systems are still fine after 30 years.Flex is more restrictive ,which when sized correctly will result in larger ducts compared to metal,with the same result for air flow.

    Many on this site are stuck on metal,but the real jury is still out.

  7. #7
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    Quote Originally Posted by dash View Post
    We are in Florida ,flex systems are still fine after 30 years.Flex is more restrictive ,which when sized correctly will result in larger ducts compared to metal,with the same result for air flow.

    Many on this site are stuck on metal,but the real jury is still out.
    how would you get flex in a wall cavity? 2X10 walls? Flex installed properly may be fine, but if I have my choice of duct it will be hard piped, I realize flex is better for the bottom line, and in an attic like most of your installs down in the tropics, but in my book the only place it belongs is in an attic. Or that really nasty crawlspace on a retro job, cause I ain't crawling back there
    You can't fix stupid

  8. #8
    Join Date
    Oct 2006
    Location
    Georgia
    Posts
    48
    Quote Originally Posted by dash View Post
    We are in Florida ,flex systems are still fine after 30 years.Flex is more restrictive ,which when sized correctly will result in larger ducts compared to metal,with the same result for air flow.

    Many on this site are stuck on metal,but the real jury is still out.



    Go with metal. It will give you many years of comfort and joy . Yeah I'm in the christmas spirit !
    <*}(((-< Good work is not cheap!
    >*}(((-< Cheap work is not good!

  9. #9
    Join Date
    Nov 2007
    Location
    San Marino, CA
    Posts
    5
    thanks for the input, I think I'll be putting this contractor's bid in the round file.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Nothing wrong with using flex if its installed tight.
    Sheet metal can be real loud when installed wrong.

    If you want metal duct, tell the contractor you want metal, and don't mind paying the extra money it will cost.
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    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Feb 2006
    Location
    Tn.
    Posts
    1,344
    Quote Originally Posted by beenthere View Post
    Nothing wrong with using flex if its installed tight.
    Sheet metal can be real loud when installed wrong.

    If you want metal duct, tell the contractor you want metal, and don't mind paying the extra money it will cost.
    I like flex . Its quieter too . My biggest problem ever though is animals wanting to tear it up (underneath floors).When I started hvac we used all metal trunk and lines no exceptions.15 yrs Then the trend seemed to be you had to use flex to beat the bid to get the job! People just dont want to pay extra for rigid ducts it seems. If money was unlimited, mine would be all hard metal .

  12. #12
    Join Date
    Jun 2002
    Location
    Dacula, GA
    Posts
    12,624
    Quote Originally Posted by dash View Post
    We are in Florida ,flex systems are still fine after 30 years.Flex is more restrictive ,which when sized correctly will result in larger ducts compared to metal,with the same result for air flow.
    Many on this site are stuck on metal,but the real jury is still out.
    The trick is to size it correctly. For the same friction factor for a given cfm of air through flex duct compared to round duct you have to go up typically 2 sizes. 4" to 6", 6" to 8" and so on.
    "I could have ended the war in a month. I could have made North Vietnam look like a mud puddle."
    "I have little interest in streamlining government or in making it more efficient, for I mean to reduce its size. I do not undertake to promote welfare, for I propose to extend freedom. My aim is not to pass laws, but to repeal them. It is not to inaugurate new programs, but to cancel old ones that do violence to the Constitution."
    Barry Goldwater

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