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  1. #1
    Join Date
    May 2007
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    Rectangular v. Square Metal Duct

    I very recently had a new system installed in my apartment. I had the old duct board replaced with metal and when I went into the attic I was surprised to see that all the new ducting was circular rather than retangular. The contractor explained that round is better as there is less air resistance and this seems to make sense. Is there any reason why rectangulr would be better?

    Separately, I was also surprised to see that the ducting (which is in the attic) was all elevated about 20 inches or so above the joists, whereas the old ductboard was attached flush ontop of the joists. Is that ok? What are the pros and cons of such an approach?

    (BTW, title should read Rectangular v. ROUND Metal duct)


  2. #2
    Join Date
    Aug 2002
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Round doesn't have less resistance to air flow then the equivelent size rectangular/square duct.

    Round does take less metal ,for the equivelent size duct.14" round equals
    13.5 X 13.5 Sq or 25X7 rectangular.So the farther away for sq. the more metal it takes to handle the same amount of air.

    Round is prefabed and less costly ,can use a lighter gauge metal,takes slightly less insulation to wrap it as well..

    Nothing wrong with round ducts ,at all.

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