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  1. #1
    Join Date
    Nov 2012
    Location
    Bentonville, AR
    Posts
    1

    Return Air Velocty

    What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by Gary Swanson View Post
    What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?
    First, I locate where the returns are going, then I size the ductwork accordingly. If I'm working with a 4 ton (1,600 cfm) blower, I'll design at least 1,800 cfm of return air grilles.

  3. #3
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,914
    Quote Originally Posted by Gary Swanson View Post
    What is a good rule of thumb for designing return air ductwork. Is there a recommended maximum velocity and static pressure?
    Manual D says the Maximum Return side FPM for Flex duct should be:

    Return Grill face velocity - 500 fpm

    Filter Grill face velocity - 300 fpm

    Trunk and Branch Ducts - 700 fpm

    Conservative velocities:

    Trunk and Branch Ducts - 600 fpm

    Return and Filter Grill stay the same as listed above.
    Instead of learning the tricks of the trade, learn the trade.

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