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  1. #14
    Join Date
    Aug 2008
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    416
    As to your spacing question. In my home and what I've seen in others they are minimally spaced about 16" apart which coincidently is the floor joist spacing . And sometimes they are two takeoffs in the same joist bay (one going left, one going right). That said there is one feature of the trunk that somebody knowledgeable maybe designed, and that is that every so often (say 8 - 12') the trunk steps down a size. I beleive this is done to keep up pressure at the takeoffs closer to the furnace. So if you were creating a duct system from scratch a pro designer would be a good thing.

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,337
    Quote Originally Posted by ace064 View Post
    wraujr- I do not feel highjacked at all. Keep sharing your ideas. We are all here to learn and share our experiences.
    Along these lines about high and low returns, is it proper to vent thru the 16 inch wide space between studs and place both high and low covers that are closeable. That way you can use the high one in summer and the low one in winter. The exit would be out the bottom area of the wall space into the air return trunk. Is this crazy or does it make sense?
    Wall cavities aren't always sealed. So you can pull in attic air.
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  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,337
    Quote Originally Posted by wraujr View Post
    I have no advice or opinion. I bet this is one of those things you ask five pros and you get five different answers. But if some HVAC industry lab set up a test room with vents and smoke gens and a stack of calibrated thermomer every 12" in altitude, you'd get a proof positive answer and this would never be debated again (like it has on this site before). Thats why I asked if anyone knew of a study...

    I live in a house with floor vents and central return in hallway ceiling. I don't notice any layering/stratification, etc.
    I also work in a office with supply vents AND return in 9' ceiling and once again I notice nothing. I'd like to see science provide an answer...(with data please)
    ACCA did do test on how much the position of a return makes. Minimal to no effect on comfort.

    Remember, air is "pushed" into the return, not pulled.
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  4. #17
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,096
    Quote Originally Posted by beenthere View Post
    ACCA did do test on how much the position of a return makes. Minimal to no effect on comfort.

    Remember, air is "pushed" into the return, not pulled.
    Yep.

    I seem to remember seeing that documentation on this site as a matter of fact.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

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  5. #18
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,337
    Quote Originally Posted by hvacvegas View Post
    Yep.

    I seem to remember seeing that documentation on this site as a matter of fact.
    As I recall, it was Dash that posted it.
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  6. #19
    Join Date
    Dec 2002
    Location
    Arizona
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    4,416
    Quote Originally Posted by timebuilder View Post
    Ceiling fans are great at getting the warm air down to where the people are in winter.
    Yep, I agree and just that is recommended in manual D.
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  7. #20
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,235
    about duct location on the plenum.

    in my climate (hot humid) putting the ducts too close
    together, where the outer liners are in contact with each other
    will cause condensation.

    also if duct take offs are too close to each other it will be
    a pita to properly mastic seal the take off, the inner liner
    and then the insulation and outer jacket.

    if the insulation and outer jacket are not in contact with the
    plenum then the exposed duct take off will condensate.
    as will all of it if not sealed.

    mastics last. duct tapes fail.

    I usually install a 4' plenum instead of a 3' just
    to have the space around the ducts.

    just my own experiences but I don't tap off end cap
    or too close (within 18") of ahu/coil.


    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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