Trunk takeoffs

[lginla]

Here is what I think is a basic question about how to transition from furnace plenum to individual ducts:

I am putting in a new furnace in the attic. There are four 12" diameter flex ducts going in various directions from the furnace and feeding the different rooms. Two ducts are vertical, to supply the first floor, while the other two are horizontal in the attic, to supply the second floor.

The horizontal furnace will discharge into a 20"W x 23"H x 30"L plenum. The plenum will T-bone into another horizontal plenum, or short trunkline if you will - it will be approximately 20"W x 16"H x 60"L. The 12" flexducts will be attached to this second plenum.

The two vertical ducts will feed off the bottom of the long horizontal plenum. The other two (the horizontal ones) were originally fed off the ends of the plenum, as shown below:

.........._______________________________________
.._____l..............................................................l____
..l.......l..............................................................l.......l
..l.......l.........................PLENUM...........................l.......l
..l_____..............................................................l____l
..........l_______________________________________l
....................l...............l...........l...............l
....................l...............l...........l...............l
....................l_________............l_________l


But I wonder if it is OK to take off from the plenum ends, or should all four ducts take off from the sides of the plenum to have more even air distribution, as shown below?


..............__________...........__________
..............l...............l...........l...............l
..............l...............l...........l...............l
....______l__________l______l__________l______
....l..............................................................l
....l.........................PLENUM...........................l
....l..............................................................l
....l_______________________________________l
..............l...............l............l...............l
..............l...............l............l...............l
..............l_________l.............l_________l

Or is the original configuration fine?

Thanks,

Leon

[Jay11J]

The orginal set up is fine.. if you do the "new" on, the flex wil have to come back down, and it may kinck and cut down on the air flow.

[lginla]

Jay,

Thanks for the advice, it certainly makes sense. Also, thanks for taking the time to read and understand my words and poor attempt at a sketch - you are right, the latter approach would require two elbows or turns, which seems like an unnecessary drawback - thanks for taking the time!

Leon