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ductwork moving question

Posted by squishyball (My Page) on
Fri, Mar 8, 13 at 10:48

I have a question for you all.. here's what we've got...
Residential 2-story. 20x8 mainline perpendicular to and under the joists. Transitions to 16x8 about halfway, then to 12x8 via a curvy transition. Most taps are 6" rounds, coming out the top and running between the joists. The final 12" section ends with one tap right near the end out the side, and one out the end. This end tap is the longest run of the house, to the biggest room on the 2nd floor (mast bdrm). The other run, out the side right at the end, goes to the 2nd flr mast closet.

I need to move some of these cuz they're in the way of finishing a basement window -- and I see basically two options.

1) tear out the 12x8 transition, just cap the 16x8, then take the two runs out the side of the 16x8, one at maybe 12" then 20" back from the end. Doing this might see less air going out that most important run to the 2nd floor master, as it will just be a normal side tap with a twisting long run instead of an end tap.

2) take out the 16-12 transition, cut the 16" section back the distance I need (about 2') then reattach the 16-12 transition, and again come out the end and side of that. This will keep the endcap tap, altho some ppl seem to not like this.

We have no problems currently. The end tap does not seem to cause us lower flow elsewhere, tho I can't compare cuz it's always been that way.

Is the 16-12 transition creating back pressure for the rest of the taps in the 16" section? If so, then the end tap might be just fine. If (1) is preferred, then why wouldn't the original contractors who built the house have done it this way? It would have been less expensive than putting in a 16-12 curvy transition, requiring no special parts. Or was that transition and subsequent end tap appropriate to promote flow to that furthest and most imporant leg?

Thank you!

Follow-Up Postings:

RE: ductwork moving question

I would keep the transition in place as this is likely how the contractor designed the system for balancing purposes. Although it is frowned upon to "take off" a run within 18" of an end cap. Perhaps this was part of the plan so more air would get to the 2nd floor. I would assume a inline damper would at a minimum be installed so that it could be adjusted if it was found to be stealing too much air flow from other parts of the system. If so you can test your theory but shutting it right down and see how the rest of the house responds.
Another advantage to keeping the transition is now you won't have to buy more 16" ductwork and cut holes / lengths. If I picture this correctly all you would have to do is extend some of the 6" runs so they will now reach the shortened transition piece.

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