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  1. #1

    what is a sub duct?

    ive been in commercial/multi-family dwellings for 3 years but because of my ability to pick up fast ive been promoted to job supervisor( i have 8 years in residential total 11 years in the field). any way my new jobsite has 27 E/A risers in 2 hr rated shafts but no fd/sd. the engineer said i have to sub-duct them... from what i understand its when you tie into the riser on a 45 is that it? i would just use to 45s i just wanted to make sure before i measure up for production.. thanks guys

  2. #2
    Join Date
    Aug 2012
    Location
    Gainesville, FL
    Posts
    325
    In some situations you can't always pipe every exhaust directly outside, and you can't use dampers on grease or lint. The solution is to duct into a rated duct. There are other applications as well, but this is probably the most common.

    The unrated duct basically penetrates and turns up 2 feet inside the rated shaft, hence the sub-duct. Smoke/fire coming from other penetrations won't be able to make a u-turn and travel back down. Kind of like a p-trap for smoke. I've not seen them on 45. Ask for a detail from the eng. it will save your guessing. It's not really a common thing so the building official will likely pick it apart.

    http://subductriser.com/faq_fill.php

  3. #3
    Its designed for 5-6 dart fans per rider most of the riders are 8" x10" or close the architecturials don't give ne enough room to make the shaft 2' bigger... all the riders tie in to a bigger trunk running to a exhaust fan then to a large louver.... some of the riders have basic rnd pipe tapping off others have 8"x6" tapping off to catch more than one fan.. does that help?

  4. #4
    Join Date
    Aug 2012
    Location
    Gainesville, FL
    Posts
    325
    You penetrate the side and turn the sub duct up into the rated vertical shaft. The shaft should already be sized by the eng. and you won't have to make it bigger. The vertical trunk with a fan on top is the rated shaft.


  5. #5
    We'll that helps a little thank you

  6. #6
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,998

  7. #7
    Join Date
    Aug 2012
    Location
    Gainesville, FL
    Posts
    325
    Sorry I'm on a mobile looked like tech to tech type question

  8. #8
    My apologizes. Im new to the site ty again

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