Return air sizing
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  1. #1
    Join Date
    Jul 2005
    Posts
    12
    I am having a new 5 ton 14 SEER AC being installed today in a 2500sqft home. There is a single return air sized at 20" x 25". Is this big enough? I've heard 100sq" per ton and 200sq" per ton. Which is correct?

    Thanks
    Robert

  2. #2
    Join Date
    Feb 2005
    Posts
    19
    Is it a stamped face return grille? Or a filter grille?

    Sounds like even if it is a stamped face grille it is more than a ton undersized....

  3. #3
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584
    Originally posted by bubstang
    I am having a new 5 ton 14 SEER AC being installed today in a 2500sqft home. There is a single return air sized at 20" x 25". Is this big enough? I've heard 100sq" per ton and 200sq" per ton. Which is correct?

    Thanks
    Robert
    It really depends on the size of the ductwork attached to opening.
    But, if your using rule of thumb method 144 sq.in. per ton or 24x6-x5 will give you a close estimate.
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  4. #4
    Join Date
    Jun 2002
    Posts
    460
    A single return results in poorly balanced airflow. They can also be noisy.

    IMHO, you should have a return in almost every room in your house (except for the kitchen and bathrooms).



    [Edited by JoeSix on 07-26-2005 at 02:53 PM]

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    24X30 without a filter in the grille,25X40 with one in it.


    With a return that small did you have a five ton system before ??


    What size duct connects to the grille and the furnace/air handler??

  6. #6
    Join Date
    Jul 2005
    Posts
    717
    To be on the safe side, make sure you have at least a total return 10% minimum larger than the supply total.
    Example; If 400 sq in supply out, you need a min. of 440 sq in return.

  7. #7
    Join Date
    Jul 2005
    Posts
    12
    The grill is a stamped grill with a filter in it 20"x25" and the duct is a 16" round.

    Thanks

  8. #8
    Join Date
    Jun 2000
    Location
    N. W., IN
    Posts
    1,017

    Frown

    16" return duct for 5 ton a/c.
    All together now, "not gonna' work"

  9. #9
    Join Date
    Jul 2005
    Posts
    12
    It's been like this since 1976 and I'm making some changes. Don't want to dump to much into it cause I'm going to try and sell the place in the next 1-2 years.

    Yes it was a 5 ton previously.

    What's your thoughts on the duct size? 20"?

    Thanks for all the input.

    If any of you are in the Spring, TX area, let me know.


    It appears the airbox gets reduced down to an 18" square inlet to the furnace and then 16" round duct to the return air. Not sure I'm calling these things right, but hopefully you know what I mean.

    Thanks again!

    [Edited by bubstang on 07-26-2005 at 04:53 PM]

  10. #10
    Join Date
    Feb 2005
    Posts
    19
    If you weren't wanting to put much money into it then why did you invest more for a higher SEER that won't work with your return?? You could have put in a lower SEER and did the duct repair for probably close to the same price. I understand you not wanting to put much money into it, but it is a case of either working, or not. In my opinion you don't have a choice as to whether or not to spend more money to fix the return. Eiether you just paid for a new system that will work, or won't work. You choose. It is a no brainer.

  11. #11
    Join Date
    Jun 2000
    Location
    N. W., IN
    Posts
    1,017
    20" would be a good idea. In Texas that must be one hard working system.

  12. #12
    Join Date
    Jun 2002
    Posts
    460
    Originally posted by bubstang
    the duct is a 16" round.
    Wow. Even if you could make that work, that's an air speed of 24 ft/second through that duct at 2000 CFM.

    (Not to mention 10 ft/second through that grill opening)

    Whooooosh!

  13. #13
    Join Date
    Jul 2005
    Posts
    12
    It appears the airbox gets reduced down to an 18" square inlet to the furnace and then 16" round duct to the return air. Not sure I'm calling these things right, but hopefully you know what I mean.

    You guys want pics?

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