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  1. #1
    Join Date
    Jan 2006
    Im designing a home with engineered joists. The heating will be forced air, and centrally located in the basement. It is a two story house.

    The basement is rectangular (widest span is 17') and about 70' long. Can anyone offer any suggestions on how to layout the joists to make it the easiest for the HVAC guys?

    Thanks for you help.

  2. #2
    Join Date
    May 2004
    Rapid City, SD
    By engineered I'm assuming the BCI style joists (looks like a wooden I beam).

    If so, there's not much you can do really. The duct will most likely be below the joists for the majority of the run. Takeoffs will probably come out of the top and run in the joists, sometimes cutting a hole in the joists to get across the bays.
    If you have a choice go with a larger truss, once they get down to 12" or less it gets tricky to run duct big enough.

    If it's webed truss's, just do your best to make sure all of the triangles line up, which is more of the architect's/designers job.

    Maybe I've been blessed with good builders lately, but honestly I haven't ran into too many houses that were a major pain to run duct in.

    If all else fails, put a 9' celing on the lower floor so you won't loose much headroom when you encase the duct in chases.
    "If you call that hard work, a koala’s life would look heroic."

  3. #3
    Join Date
    Feb 2003
    to get the best design, do a complete house design, then let a HVAC designer do a system for both a 1 & 2 story.

    the trunk line may be rectangular & would run perpendicular to the joists, with circular branch ducts. a trunk line in a chase would be the likely feeder to the second floor.

    keeping all ducts in the conditioned space makes the most efficient system.

    get a copy of ASHRAE Fundamentals & do the exercise yourself, then have the HVAC designer critique your solution.

    to understand the heat loss | gain, you can also run the load calculation program from this site -- = few $

    THANKS for asking while the project is still lines on paper!
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  4. #4
    Join Date
    Nov 2004
    SW FL

    Thumbs up RISERS

    Originally posted by linz
    Heating forced air, centrally located in the basement, two story house, 17' x 70'

    Can anyone offer any suggestions on how to layout the joists to make it the easiest for the HVAC guys?


    Make a taller ( 13 or 14 [ 112" total] bricks)
    basement with a soffit concept
    in mind for later finishing of the basement.

    ~8'10" (106") ceiling throughout
    except for duct soffit area

    For Starters: 4 Zones, 2 Zones for each story
    Run about seventeen feet horizontal each direction
    (half of 35-foot total x 2 ) for both supply and return.

    Two risers (1 Supply & 1 Return) each story =
    4 Supply Risers and 4 Returns = 8 Total

    Or half that if the first floor air diffusers are in the floor which is normal for northern climate
    and you are not planning on A/C.

    ~1,000 CFM to each floor, 500 CFM each riser
    500 CFM .. 14" x 8" (or 18" x 6") duct
    Specify two vertical chases
    (~ 20" x 14" total area for supply & return)
    through the first floor.

    Send .DWG floor plans with preliminary joist detail
    for a 3D HVAC design with
    proper air flow and ducts to each room.

    See you later.

    [Edited by dan sw fl on 01-24-2006 at 05:12 AM]
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Feb 2004
    Now that you have all the high tech answers I'll submit the correct answer. You should run the floor joists the short way, ie the 17' dimension, to make the Hvac job easiest to run and make system work the best. It also will make framing less of a nightmare foe the framer. One bearing wall down the center of the building is a heck of alot easier than three walls perpendicular to the building.Talk to a couple of framers and see what they say.
    I am the "Wally". All others are meer imitations of the original.

  6. #6
    Join Date
    Jul 2005
    hey Wally,duh, did you really think he was going to run them the 70' way.?

  7. #7
    Join Date
    Feb 2004
    Set your drag a little lighter there Deejoe. Out of the 50 + houses I did last year, 4 of them were with floor joists run the long way. I couldn't tell you how many I have done over 30 years that have been run the long way. And then the builder puts the mechanical room in the end of the house so all the runs are crazy long. What a nightmare.
    I am the "Wally". All others are meer imitations of the original.

  8. #8

    Thumbs up

    He's right. The last thing I would have expected is for someone coming on the site looking to tailor make construction for HVAC! It always works the other way

  9. #9
    Join Date
    Jan 2006
    thanks for all the feedback!
    this is my first post, and im quite impressed.

    I should clarify, that the project is a duplex (side-by-side). So when i said it was 70' long, more correctly each unit is 36' long, by 22' wide.

    So, yes, I am planning on running the joists across the 17' direction. Again, each side has its own heating/cooling system, and the HVAC is centrally located in the basement.

    At this point, I have spec'd 9 1/2" TJI, and allowed a vertical chase directly above the furnace. My hesitation right now is where the main trunk will go and how it will affect the basement layout. I am assuming it should run down the centre (or near to it) along the 36' direction.

    I would like to post an image of the plan. Is it possible to do this in this forum?


  10. #10
    Sounds like a great job for a contractor to get with someone actually giving a crap about HVAC considerations.

    Yes, you can copy and image and show it on the thread.

  11. #11
    Join Date
    Jul 2005
    Linz; The ideal duct layout in your situation would be to run the main supply and return trunks at right angles to the joist direction.
    Supply runs off the top,within the joist spaces to boot and register.

    Return air;joist lining (if permitted)from top of main trunk along joist path to floor return stud space.

    NOTE; when roughing in for the supply, locate floor registers at outside walls.
    When roughing in for return, locate the grilles on an interior wall's stud space so that you can have both LOW or HIGH return air intake (same stud space) depending on the season (heat/cool). For this low/high to work, install a dampered grille on the low opening, and install a damperless grille on the high opening.
    Heating season;the low dampered is open,thus blocking off the high intake grille.

    Cooling season; the low dampered grille is closed allowing the high grille to draw air.
    make sure this stud space is girtless,etc.(clear)

    Hope this helps.Good luck with the project.

  12. #12
    Join Date
    Jan 2006
    thanks again for you help!

    I have a joist layout i'd like to post as an image. I can't find a place in the post to upload the image though. What am i missing?

  13. #13
    Mod01 Guest
    You can't do a direct upload. You'll need to have the image file hosted.

    Follow these instructions.

    You can use the image hosting site of your choice.

    [Edited by Mod01 on 01-24-2006 at 02:16 PM]

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