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    ryan0804's Avatar
    ryan0804 Posts: 2, Reputation: 1
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    #1

    Apr 6, 2009, 10:44 PM
    AC return vent size
    Maybe you can help me. My home has 2 zone heating/cooling. The AC units are 3 ton and 3.5 ton. I live in Arizona. Liquid lines were swapped out last year with 3/8" since 1/4" was the wrong size. The return vent hoses (1for each zone) are 16" round. The 3.5 has a 20x24 diffuser vent cover. The 3 ton has a 24" square one. I had readings on the 3 ton unit. He measured 575cfm. Would it help my efficiency to run an ADDITIONAL 12" flex return line to the air handler?
    Joshdta's Avatar
    Joshdta Posts: 2,549, Reputation: 45
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    #2

    Apr 7, 2009, 04:22 AM

    Yes it deffentally would you need to have 400 cfm per ton of cooling, so 1200 for 3 ton and 1400 for the 3 1/2.

    16 in duct is supposed to carry around 1400 cfms if it is installed right with no kinks or bends. How ever inless you have a free flowing return air grill I dought the registar is allowing that much. Is you filter in the air handler or at the return grill?
    ryan0804's Avatar
    ryan0804 Posts: 2, Reputation: 1
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    #3

    Apr 7, 2009, 10:59 AM
    The filter is on the grill section. Would I benefit from installing a secondary 12" return vent? Thanks!
    Joshdta's Avatar
    Joshdta Posts: 2,549, Reputation: 45
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    #4

    Apr 7, 2009, 11:03 AM

    Yes you will get lots better performance from your system. I would think that a 10 in would do you fine.
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    acetc Posts: 1,004, Reputation: 79
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    #5

    Apr 9, 2009, 06:58 PM

    I might add to the above posts that in order to move air one must also take into consideration the size of the supply ducts as well as the return, a sixteen inch duct only moving 575 cfm tells you that you have other issues. Good luck, Mike
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