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Thread: to mark beiser

  1. #1
    42yrs exp is offline Professional Member BM -bad email address
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    Your answer to "why do you want to know."

    On a 3 ton attic job some of the guys I know in the business will use 7 (or 6) flex duct to the rooms in the house. So, using the duct calculator using .10 friction per 100 ft. a 7 inch duct will supply about 160 CFM to a room.

    I was wondering how many Btu's per hour will be removed from the room under those conditions?







  2. #2
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    Originally posted by 42yrs exp
    So, using the duct calculator using .10 friction per 100 ft. a 7 inch duct will supply about 160 CFM to a room.
    There is a good possibility that the airflow is nowhere close to 160 CFM.
    These guys are creating a tremendous business opportunity for you by installing duct systems this way.
    Have you set up a Google alert for Carbon Monoxide yet?
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  3. #3
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    Depending on the length of run, that 7" could be delivering 180 cfm, or 120.

    They make a duculator for flex, you should order one.

    As I'm sure some one may have told you already, if you do a room by room manual J, that will tell you how many cfm, each room requires.


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  4. #4
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    Originally posted by beenthere
    Depending on the length of run, that 7" could be delivering 180 cfm, or 120.

    They make a duculator for flex, you should order one.

    As I'm sure some one may have told you already, if you do a room by room manual J, that will tell you how many cfm, each room requires.

    A manual d will tell you what friction to use, which will tell you what size flex to run.


    That is, if you want to go by the book.

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  5. #5
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    It's not the length of the 7" run that determines the cfms delivered.

    Check out Man. D @ http://www.acca.org

    It's the total equivalent length of the longest supply and return path,which determines the Friction Rate to use on the ductolator,which tells you how many cfms a 7" flex can deliver at that FR.

    7" flex,is likely somewhere beteen 80 to 120 cfms,per a flex ductolator.

  6. #6
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    Originally posted by dash
    It's not the length of the 7" run that determines the cfms delivered.

    Check out Man. D @ http://www.acca.org

    It's the total equivalent length of the longest supply and return path,which determines the Friction Rate to use on the ductolator,which tells you how many cfms a 7" flex can deliver at that FR.

    7" flex,is likely somewhere beteen 80 to 120 cfms,per a flex ductolator.
    LOL... Ok, I'll sit corrected.
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