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  1. #1
    Join Date
    Sep 2005
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    i've been doing commercial duct work for a while. i always do well on the work i am assigned, but i always have the prints to show me what to do. i just told a friend i would run the duct work in the house he is building and was shocked to see his prints had no duct work on them. now i have no idea how to figure out materials. how many CFMs does each size round duct carry? i have a 3 1/2 ton unit with both plenum sizes 14 1/2 x 14 1/2, unit specs is 1150CFMs and the house is 1512sqft. how do i figure out my materials given this information.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    40,528
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    Some flaws here.

    He must be building it pretty poorly to need 3.5 tons in a 1500 sq ft home

    Also, you say unit spec is 1150 CFM but for 3.5 tons ought to have more capacity than that.

    First, someone needs to do an accurate heat gain/loss calc. If it really needs that much cooling, he should build the place right to reduce the gain & loss. That's sorry for new construction.

    Then get a hold of ACCA's Manual D and study it. Butcher his duct system and he'll remember you for life - or at least as long as he is in his uncomfortable house.

  3. #3
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
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    You never have any HVAC drawings on blueprints for residential, well I can't say never, once in a while the architect will draw all his/her oversized crap, your kinda screwed, time to go back to school and learn calculation & design classes or pay someone to come out and design it for you while you do the labor.

  4. #4
    Join Date
    Jun 2004
    Posts
    47
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    id pass if i were u

    cuz it sounds like your in over your head and if it goes wrong you just lost a friend..
    If its worth doing, it's worth doing right.

  5. #5
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,731
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    Originally posted by BaldLoonie
    He must be building it pretty poorly to need 3.5 tons in a 1500 sq ft home
    Either that or he likes it 68 degrees in the house on a 105 degree day. We fat people sweat a lot. ;^)

  6. #6
    Join Date
    Sep 2005
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    Thread Starter
    ok well thanks everybody

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,736
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    Exclamation Too much Capacity

    Originally posted by kipfisher
    How many CFMs does each size round duct carry?

    i have a 3 1/2 ton unit with both plenum sizes 14 1/2 x 14 1/2, unit specs is 1150 CFM and the house is 1512 sq ft. how do i figure out my materials given this information.

    CFM per duct size = ~ 600 FPM * Duct Area ( Sq.Ft.)

    Send me drawing + Window Schedule and SHGC
    and I'll tell you CFM per room.
    Location : ____ ?

    I'll re-check capacity ( 26,000 BTU h Sensible ? ) required.

    [Edited by dan sw fl on 09-21-2005 at 08:37 PM]
    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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