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  1. #14
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Originally posted by chaddawson
    Oh my goodness.

    I'm sitting here trying to visualize the air currents inside this contraption. I'm thinking the air enters from the oval, strikes the bottom of the box, flows out primarily in several directions along the bottom, curls up along the sides, circles back along the top, and then strikes the additional air trying to enter. And it's not doing this in a nice neat fashion, since even in good ductwork, airflow is seldom laminar. The turbulence going on inside this thing is unreal. Friction loss sky high.

    I guess some folks think all you have to do with ductwork like this is take a sheetmetal box and charge it with air pressure, and something will flow out the holes. Yeah, you'll get flow, but at a severe penalty to velocity. Here I was obsessing over the oval vs. the 12" round, only to see what kind of box it's flowing into! I'd be curious to run some numbers on that puppy!

    At a bare absolute minimum, if the 12" round entered the upper end of the box (not the top as pictured) and the take-offs were cut into the far side of the box, it might flow a LITTLE better. Not much, but an improvement. But apparently since this 12" round is draping down from the attic and then being faced with the small amount of space between the drywall and the underside of the top floor, WTF are you supposed to do with that?

    Me? Being a two story house I'd not consider trying to cool two floors with one unit. I'd also never put any equipment in an attic. Not even ducts. Air handlers in closet or drop ceiling, ducts in drop ceiling, below attic insulation, IN CONDITIONED SPACE!

    But...you're in Phoenix. And...you're not alone. Do a search on this site for a pro member named PaysonHVAC. He's a Phoenix tech and he's filled the Wall of Shame section of this site with infamous Phoenix installs.

    As for how to realistically solve the problem you have, looks like it ain't gonna be fun. That box, IMO, has to go. Absolutely. I don't know how the ducts run out from that box...maybe you could snap some pics for us and post them. Pics...as your drawing has...go a long way.

    Meanwhile, when I hit the books and calculator again, I'm gonna play around with your scenario more to teach me some really good object lessons. I'm glad I've helped, in whatever way that was.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  2. #15
    Would like to send pictures but the confined space this box is in makes it impossible to get decent shots. Also, I only have acces to half of the top side of the box. The rest of the dimensions I got by removing the 12" duct, and sticking my arm and/or a ruler in teh box. That's why I don't have accurate measuremetns for the placement of the ducts coming off the side of the box. But Im certain of the size of those ducts.

    I'll try to locate the guy you recommend. Would love to make the wall of shame!

  3. #16
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    The main problem with the box is that it's oversized,plus the 12" needs to be round not oval.

    If you can correct those two thing it will improve air flow,maybe enough or maybe not .Can't say that you don't have other duct issues without a ton of information or being there.

    Your idea of filling the bow internally would help,but I not sure what you could fill it with ,mainly due to the limited access you have.


    FYI--The box being over sized doubles to triples the equivelent length of that fitting.

  4. #17
    Is this something I could reasonably argue with the registrar of contractors as being improperly done and have the installation company fix at their expense?

  5. #18
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    I doubt it,as there's probably no code violation .

    Now if the code specified that the duct work was to designed per Manual D,then maybe.Flordia code requies Man d,but the inspectors would know if it was right or wrong ,for the most part.

    I'd talk to them about fixing it for you,providing them some evidence that it's wrong.I'd bet they they really don't understand why it's wrong,may even be good guys and decent techs otherwise.

    Next step,if you choose,would be to get a local Pro,to document the problem ,the fix and before and after static pressure and air delivery,and go to small claims court.Probably not worth the expense,time,and agevation,IMHO.

  6. #19
    Join Date
    May 2006
    Location
    Raleigh,NC.
    Posts
    350

    bandaid

    i have improved simular problems when ducts where inaccessable. have your hvac company come out and install a 14" duct with damper and reduce it to 12 at the last point of access.
    remember, with electronics; when its brown,its cooking and when its black, its done!!!

  7. #20
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836

    Re: bandaid

    Originally posted by micdundee
    i have improved simular problems when ducts where inaccessable. have your hvac company come out and install a 14" duct with damper and reduce it to 12 at the last point of access.

    Mic's correct, this will help .

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