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  1. #1
    Join Date
    Aug 2008
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    Return Duct Sizing Question

    The AC professional says I have a bottleneck in the return for the downstairs AC unit. The unit is a 4 ton. Because of the way the house is constructed there is not a direct opening from the return air filter to the air handler. It makes a turn and goes between the floor joists for a short period. I measured the opening at 24" x 11". He recommends adding two 12" x 24" returns. Does this sound right??

  2. #2
    Join Date
    Aug 2002
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    He's likely right,though you may not need to add that much.

    The size of each duct in your system is determine by the overall resistance of the duct system,based on actual length(logest supply and return duct),plus the equivalent length of all turns,elbow,fittings ,grilles,etc.,and the available static(ability to move air) of the indoor blower.

    So it' impossible to tell from here.

    If he took static readings,our the temperature rise of the furnace,or an alternate method,he could tell quickly that you have an issue.

    My guess is to trust him,most wouldn't suggest doing something like that if it wasn't needed,and few are trained to find these issues.If he was selling some add on,quick and easy to make a buck,I'd be more cautious.

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