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  1. #1
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    Dec 2019
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    Question about Trunk Routing

    Hi, full disclosure, I have virtually no HVAC experience...trying to learn! I am currently working on the layout of a new construction house with my architect. The last house I built ended up with soffits everywhere, so I'm trying to be more careful this time around.

    The house is a single family city rowhome. 2600sqft, 4 stories, 38' high. I'm planning to do dual zone HVAC.

    In an ideal world. I'd have both inside units located in the basement. One unit would service the basement, first floor and second floor (roughly 1600sqft of area). The second unit would service the third and fourth floors (roughly 1300sqft of area). I attached a rough schematic of the basement layout. The issue I'm having is that I can't run the trunk the full length of the house because there's an inaccessible area of the basement. What I'd like to do is have two elbows in both trunks to allow them to "climb" from the basement to the first floor where I would then have a soffit in the garage that would allow for branches to reach everywhere. The bottom wall in the dragram will be framed with 2x6s.

    The maximum reach from the basement furnace to the top floor is roughly a 35' run (assuming I do floor registers on the 4th floor).

    If I can't do the elbows in the trunks, I'll have to move the furnaces up to the 1st floor. There's also a spot on the 3rd floor where I can locate the 2nd furnace if that positioning helps things.

    Any insight would be very helpful. I'm around 5 months away from needing an HVAC contractor, but I would love to have everything mapped out now! Thanks so much for the help!
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  2. #2
    Join Date
    Oct 2011
    Location
    Gladstone, Oregon (Portland)
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    Double post

  3. #3
    Join Date
    Oct 2011
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    Gladstone, Oregon (Portland)
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    Give ductless a serious look being the stage you are at in your project, and your needs.

  4. #4
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Why are you trying to move air 4 stories? That's going to take a lot of floor space on the 1st, 2nd, 3rd & 4th Floors!

  5. #5
    Join Date
    Jun 2014
    Location
    Dover, DE
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    Why are you trying to map ductwork out without knowing what size duct needs to be be run?
    You’ll have to first run a manual D with a room by room manual J so you can get your duct sizing sorted out.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  6. #6
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    Dec 2019
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    Thread Starter
    Well, I was thinking that all the ducts would be concealed in our 2x6s. So two big trunks in the basement and then branches running through the 2x6 cavities/joist bays. If I have both units in the basement, I was hoping I would have no soffits on floors 2-3-4.

  7. #7
    Join Date
    Aug 2002
    Location
    Southold, NY
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    2 X 6 try 20 X 30 or more depending!

    Listen to Rider77
    Start with what size equipment you need THEN figure out where your putting the ducts.

  8. #8
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    Dec 2019
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    Thread Starter
    Valid question regarding duct size. I understand that this all depends on the calculations. I am mostly trying to figure out where the trunk could go and whether I'm safely able to "bend" the trunk to fit in my space - I realize that the trunk size is going to fluctuate depending on the needs of my system.

  9. #9
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    Dec 2019
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    Thread Starter
    Sorry, I meant that the branch supplies would be concealed in the 2x6s. The trunk will, of course, sit against the wall in a soffit.

  10. #10
    Join Date
    Aug 2002
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    Southold, NY
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    Quote Originally Posted by atb123 View Post
    Valid question regarding duct size. I understand that this all depends on the calculations. I am mostly trying to figure out where the trunk could go and whether I'm safely able to "bend" the trunk to fit in my space - I realize that the trunk size is going to fluctuate depending on the needs of my system.
    Quote Originally Posted by atb123 View Post
    Sorry, I meant that the branch supplies would be concealed in the 2x6s. The trunk will, of course, sit against the wall in a soffit.
    Why are you even doing this?

    Its the architects job to design the house
    The engineers job to design the mechanicals
    The architects job to NOT give enough space for either!

    You worry about colors and counter tops!

  11. #11
    Join Date
    Jun 2014
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    Dover, DE
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    I think the ducts will be much larger then you think.
    Get an engineer involved so the proper calculations are done. Even the 2X6 bays may not be large enough for some of the heat loads each room has.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  12. #12
    Join Date
    Dec 2019
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    Thread Starter
    Because I am a control freak (and an engineer), and I hate soffits. I didn't think to ask the PE to look at it...I guess that's a reasonable request.

    Just some more context, the house is 18' wide by 40' deep, with no windows in the party walls. These rowhomes are just rectangles, so you don't have huge load requirements because there are no windows along the 40' walls. Just pointing that out. I have never seen a house here not able to run supplies through the walls.

  13. #13
    Join Date
    Jun 2014
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    Dover, DE
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    Whose to say all those other houses are done correctly?
    A 2X6 stud bay isn’t enough to feed an entire floor, let alone 3 independent floors.
    You’ll need to have a chase for the duct.
    Exactly how big that chase needs to be depends on what the load calculation numbers show.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

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