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Old 10-02-2010, 03:19 PM   #1
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Need help sizing duct trunk addition to system.


I've got a 3 ton carrier 2-stage heat pump in the basement supplying the 1st story (~1300 sq/ft). I've attached an image of the current layout (top half of graphic) and proposed changes (bottom half of graphic).

I'm finishing the basement and a 4' section of trunk runs into the middle of the room. I'd like to relocate this section down the length of the wall (yellow line) in a soffit as to maximize my ceiling height. Doing this will also allow me to run my flex duct lines (all are 6") within the floor joist spaces. Effectively I'm looking at taking a 5' length of 12"x12" (OD) fiber duct trunk, shortening it to 1' and teeing it into a new 30' run of fiber duct trunk. This will obviously also affect the length of some of the flex lines that branch off of that particular trunk.

The question is how big should this longer trunk run be?
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Last edited by chryste; 10-02-2010 at 03:21 PM.
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Old 10-02-2010, 03:46 PM   #2
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Need help sizing duct trunk addition to system.


The 16X12X4 to 16X12X8 90 should have turning vanes installed in it. And then it should be continued to the new duct as a 16X12. The section that has 5 supplies should be about 12X12, and the section with a single 6" supply about a 8X6, or 8X8.

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Old 10-02-2010, 04:00 PM   #3
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Need help sizing duct trunk addition to system.


Quote:
Originally Posted by beenthere View Post
...The section that has 5 supplies should be about 12X12, and the section with a single 6" supply about a 8X6, or 8X8.
So since the new 30' section along the wall will be two different sizes, should the t-junction be the 12x12 you suggested or the 8x6/8? I'm assuming the 12x12 is probably what I should tee into the 16x12. Also you mentioned turning vanes in the existing 90 however that section is an existing section so I'm hoping there's already vanes in there but I'll be sure to peek down there before connecting the new section. I'm also assuming turning vanes in the tee with the new 30' section would be wise as well.
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Old 10-02-2010, 04:08 PM   #4
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Need help sizing duct trunk addition to system.


Very doubtfull they put vanes in that tee.

The new tee can be made 12X12 X 8X8 X 16X12, and it should be vaned also. other wise. The first supply on the 12X12 side, may not get much air due to turbulence.
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Old 10-02-2010, 09:15 PM   #5
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Need help sizing duct trunk addition to system.


I get what you're saying but I'm still not sure exactly where you're saying the 16x12 will tee into the new section. Will it connect into the 12x12 half of the 30' section or will it connect to the 8x8 half? I've attached another diagram showing the new 30' section (shaded) reducing from 12x12 to 8x8 and how I currently have it connecting to the 16x12. Would this be accurate?
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Last edited by chryste; 10-02-2010 at 09:23 PM.
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Old 10-02-2010, 09:22 PM   #6
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Need help sizing duct trunk addition to system.


I think I just realized what you're saying. I've attached another image showing what I believe you're saying I should do. I should run the 16x12 all the way and then run each section of the 30' run off of it instead of my previous illustrations.
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Old 10-03-2010, 02:59 AM   #7
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Need help sizing duct trunk addition to system.


Yes, your second pic is what I was saying.

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