What is the rule of thumb for the number for return grilles?
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  1. #1
    Join Date
    May 2010
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    New Jersey
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    What is the rule of thumb for the number for return grilles?

    Commercial office building with the return via a dropped ceiling plenum. It has a separate perimeter heating/cooling system (diffusers above windows) and central ventilation/cooling system with VAV boxes and diffusers. Building maintenance can install new grilles; it is just changing a ceiling tile.

    The question is, rule of thumb, how many return grilles per diffuser should a room have? Clearly at least one (there are some rooms with zero and tenants call them iceboxes). But in a room with 4 diffusers? Or in an interior room with no heating vs. an exterior room with heating?

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    5,058
    Quote Originally Posted by DavidNJ View Post
    Commercial office building with the return via a dropped ceiling plenum. It has a separate perimeter heating/cooling system (diffusers above windows) and central ventilation/cooling system with VAV boxes and diffusers. Building maintenance can install new grilles; it is just changing a ceiling tile.

    The question is, rule of thumb, how many return grilles per diffuser should a room have? Clearly at least one (there are some rooms with zero and tenants call them iceboxes). But in a room with 4 diffusers? Or in an interior room with no heating vs. an exterior room with heating?
    First Rule of Thumb;

    There are no rules of thumb.

    CFM in CFM out

  3. #3
    Join Date
    Feb 2010
    Location
    Cal
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    1,596
    Quote Originally Posted by second opinion View Post
    CFM in CFM out
    Yup. Also depends on type, perforated will move a much lower volume than egg crate. Leaking boxes and morning warm up schemes matter a bunch too. You could easily do all the wrong things for all the right reasons.

    The building owner would probably prefer it be left to a qualified service outfit rather than a building maintenance guy.

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