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Rectangular ductwork hung vertically

Discussion in 'Residential' started by kena, Sep 13, 2017.

  1. kena

    kena New Member

    Messages:
    762
    Has anyone ever seen 8"x24" rectangular ductwork hung vertically with supply takeoffs perpendicular along the 8" top? Air will follow the path of least resistance. How in the world with 24" x 8" for air to flow will it actually manage to flow through a 4" takeoff that is vertical to the air path?
     
  2. HMD

    HMD does it matter?

    Messages:
    93,136
    Location:
    here
    yep.
    had to squeeze a supply and transfer duct between walla walla and bldg beams.
    i forget what sizes. 28x10? with 10'' takeoffs, i think
     
  3. kena

    kena New Member

    Messages:
    762
    Wierd... but I'm dealing with 4" takeoffs. And since their perpendicular to the airflow, I would almost think the takeoff should be in line with the airflow, and then 90 off to a perpendicular position. I'm finding it hard to believe I'll get good air flow from those vertical takeoffs. I think most of the air will go right past them.
     
  4. pecmsg

    pecmsg Junior my ASS

    Messages:
    20,934
    Location:
    Eastern LI
    4" ain't $hit!
     
    Texas-Tech likes this.
  5. pecmsg

    pecmsg Junior my ASS

    Messages:
    20,934
    Location:
    Eastern LI
    Try angle takeoffs.
     
  6. HMD

    HMD does it matter?

    Messages:
    93,136
    Location:
    here
    whaddya call them things.............. diverters?
     
  7. MOFO the psychic gorilla

    MOFO the psychic gorilla sitting on two achers

    Messages:
    1,851
    What's the big whoop?
    Either 4" is enough or too small.
     
  8. MOFO the psychic gorilla

    MOFO the psychic gorilla sitting on two achers

    Messages:
    1,851
    HETO works real good
     
    knave likes this.
  9. flange

    flange Act like you care and do SOMETHING!!

    Messages:
    12,854
    Location:
    IMT--in my truck
    static pressure is a wonderful thing. it exerts pressure on all sides of a duct, regardless of how it is hung. I like to recommend you consider a duct as a balloon with holes in it and a fan blowing into the end where your lips would go. continue to blow into the end, the holes will release air at a given rate. with enough holes the balloon wont fully inflate.
    at any rate, your air will come out the 4 inch holes. it may come out better using laterals, turning vanes or scoops, but it will come out because your duct is pressurized.

    http://www.rses.org/assets/rses_journal/1114_Static.pdf
     
    otto, LemonWizard, Zman and 5 others like this.
  10. kena

    kena New Member

    Messages:
    762
    I'm gonna go with diverters to help give me good air flow through the supplies. What would be your recommendation for static pressure from the return to supply?
     
  11. jpb2

    jpb2 Dog Tard *

    Messages:
    47,179
    Location:
    within the bounds of reality
    Look at the blower performance chart of the machine and design from there. Make sure and allow for the filter and a wet coil
     
  12. Septua

    Septua New Member

    Messages:
    55
    Location:
    Southeast
    I'm not visualizing what you're saying, but the trunk static pressure is the force that's supposed to move the air into the takeoff/run-out...admittedly, duct geometry/configuration can be less than ideal for optimum duct performance. At the end of the day, it's available static pressure and static losses that determine residential duct system performance. You need a copy of Manual D if you don't have one...;)
     
  13. Catpower

    Catpower The Crowd Pleaser

    Messages:
    22,249
    Location:
    in the Cabana
    Flange beat me to it

    Ken if you get a nail in the sidewall of your tire does the air leak out any slower then if it was in the tread?
     
    otto and crackertech like this.
  14. Rather B Riding

    Rather B Riding Behind bars

    Messages:
    568
    Ductwork is so overlooked in this trade and the problem with a system in some cases. Learn the basics and use a ductalator. If the duct is sized properly and static pressure is maintained it doesn't matter where the take off is. Just remember never in the last 18" of the trunk line. 4" runs??? That's very little air.
     
    jpb2 likes this.
  15. newtech

    newtech 636

    Messages:
    856
    Location:
    Michigan
    Are you using a high velocity ahu!!!! like this http://spacepak.com/consumer-central-air/small-duct-high-velocity-central-air.asp

    On these you can go down to 2 inch duct. Have seen many in homes with base board heat.
     
    Rather B Riding likes this.
  16. LemonWizard

    LemonWizard Blinky Lights Wizard

    Messages:
    2,136
    Location:
    Ohighyo
    For our building controls we measure static pressure 2/3rds of the way down the duct. We measure pressure inside the duct compared to pressure outside the duct. If using a fixed setpoint its between 1 and 1.5 depending on what the balancers needs to meet flow requirements.
     
  17. Rather B Riding

    Rather B Riding Behind bars

    Messages:
    568
    Have you ever worked on these? They are a pain in the ass. They do work although they use a freeze stat to kill the condenser and the airflow is louder than they claim.
     
  18. newtech

    newtech 636

    Messages:
    856
    Location:
    Michigan
    Yep, Yep, Yep and Yep!!! But they do work!!!
     
    knave and Rather B Riding like this.
  19. Rather B Riding

    Rather B Riding Behind bars

    Messages:
    568
    Most suppliers that sell ductwork will carry these. It's a must have while laying out ductwork. Like I said 4" is not moving much air. At residential static pressure (.1) 4" delivers less than 40 cfm. You can check the actual SP. with a magnehelic manometer or a Dwyers slope gauge. You can figure approximate SP just by tonage 400 cfm per ton and duct size. Vertical or horizontal doesn't matter. In light commercial you should know how to properly size and run duct work. I have cleaned up some major f..... Up ductwork. IMG_20170914_181219214.jpg
     
  20. knave

    knave Undeterred

    Messages:
    8,166
    Location:
    Out for a rip
    You're talking about friction loss per 100 ft right? Don't forget there's a crackomatic filtrete with a .3" pressure drop and all the basement registers are shut tight.
     
    jpb2 likes this.