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  1. #1
    Join Date
    Jul 2010
    Location
    CHICAGO
    Posts
    17

    how to size a return vent for a room

    I was called to a job where the customer did some remodeling to
    a store, the customer turned it into a dance studio. she added a reception
    area that measures 12x2 x 19x8 and the height of the place is 8x9.
    When I looked at the vent setup in the reception area had 2 supplies
    and no returns. I informed them that they needed a return in order to
    circulate the air in the reception area. I put in a return, I used 8' round flex
    duct and added a perforated lay in on the ceiling. But the air is still not
    circulating. My question is should I have used rect.ductwork instead of
    round, is my return to small for the space.? I know how to check cfm
    for residential but not sure on commercial units. I brought an
    aneomometer but the instructions on it are not clear and I do not
    know how the unit works I called the company that makes it and they
    told me to go to the place where I purchased it for instructions.

    This is my second job were the issue is are flow and it has me
    confused.

  2. #2
    Join Date
    Dec 2003
    Location
    Middle of Florida
    Posts
    2,159
    What is your Static pressure drop across the coil?


    Or you can hold a thumb up to the vent if it covers the vent you are OK , if it does not you need to make it bigger!!!!!!!
    If common sense is so common how come so few of us have it!

  3. #3
    Join Date
    Jul 2010
    Location
    CHICAGO
    Posts
    17
    secorp,

    I do not understand about the thumb part what do you mean?

  4. #4
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    everything in commercial is 14" round.
    FILL OUT YOUR PROFILE!!

  5. #5
    Join Date
    Jul 2010
    Location
    CHICAGO
    Posts
    17
    Thanks for the advise Tinner 73

  6. #6
    Join Date
    Jun 2010
    Location
    St. Louis
    Posts
    159
    Also buy and learn how to use a duct calculator, these handy little things can be very useful. Of course its no good if the unit itself was sized improperly for the building or room it is heating/cooling

  7. #7
    Join Date
    Jan 2010
    Posts
    5,812
    Quote Originally Posted by tinner73 View Post
    everything in commercial is 14" round.

  8. #8
    Join Date
    Sep 2004
    Location
    Jersey
    Posts
    386
    Quote Originally Posted by tinner73 View Post
    everything in commercial is 14" round.
    that is very funny, Everything is 14", I guess all the work I did with 6"-20" is all incorrect. Well thats the rule of THUMB i guess
    Ride hard on a Harley!!

  9. #9
    Join Date
    Aug 2010
    Location
    Swamp land
    Posts
    28
    I don’t want to say to much. That way I will not get beaten up that much. The BTUH load for each room should calculate duct size.

  10. #10
    Join Date
    Dec 2003
    Location
    Middle of Florida
    Posts
    2,159

    Talking

    Quote Originally Posted by GITMO64 View Post
    secorp,

    I do not understand about the thumb part what do you mean?
    Stand back 20 feet a see if your thumb covers the vent, or break down and purchase cardboard cut outs of thumbs on E bay and use them. every five feet you back away equals 5 tons.














































    I hope you realize I am kidding......
    If common sense is so common how come so few of us have it!

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