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  1. #1
    Join Date
    Aug 2012
    Posts
    1

    enough return air?

    West Central Florida; @1200 sq. ft. conditioned space w/only 7' 4" ceilings, ranch, block construction, small attic, low pitch, currently fair(maybe) ceiling insulation, walls likely none. Air handler in attic. Original central return air grill in wall 18 x24 leading to ductboard path "under" supply plenum leading to 14" flex to return. (about 6 turns?) 2 1/2 ton unit can't keep up on the scorching sunny days. In process of eliminating wall grill and putting in ceiling with 14" flex directly to air handler. Also sealing, radiant barrier, shading window, and will be further insulating, but insulation must be last b/c I won't be able to access after.

    I realize this may only be a step at improvement, but was wondering if more return air is needed.

    Thanks for any reply.

  2. #2
    Join Date
    Sep 2008
    Location
    Largo
    Posts
    78
    Quote Originally Posted by bmcgee View Post
    West Central Florida; @1200 sq. ft. conditioned space w/only 7' 4" ceilings, ranch, block construction, small attic, low pitch, currently fair(maybe) ceiling insulation, walls likely none. Air handler in attic. Original central return air grill in wall 18 x24 leading to ductboard path "under" supply plenum leading to 14" flex to return. (about 6 turns?) 2 1/2 ton unit can't keep up on the scorching sunny days. In process of eliminating wall grill and putting in ceiling with 14" flex directly to air handler. Also sealing, radiant barrier, shading window, and will be further insulating, but insulation must be last b/c I won't be able to access after.

    I realize this may only be a step at improvement, but was wondering if more return air is needed.

    Thanks for any reply.
    2.5 tons = 1000 cfm. 14" flex = 700 cfm. You need more return. 16" flex will allow 1000 cfm.

  3. #3
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    an 18X24 grill is a bit small for a 2.5T unit. A 14" Flex is only good for ~500CFM. Depending on how it was designed a 2.5T unit is between 875 CFMs (at 350cfm/ton which is what we use here due to humidity issues) to 1000CFM's (at 400cfm/ton). So at a bare minimum we would have 2 14" ducts and usually a 24X24 grill. Remember not enough air in guarantees not enough air out. What is your supply side like. If it's not big enough then that could also be a reason it's not keeping up. A duct can only carry X amount of air through it and if its not big enough it won't matter if you have enough R/A.

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