Extending a flexible duct

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Mikey

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Pardon my introductory rant (which could be a lot longer) -- I do have a question near the end.

About a year ago, I had all my attic ductwork replaced by a large local firm, in hopes of solving a condensation problem on the branch lines, which were metal ducts wrapped in a fiberglass foil-faced duct insulation.

The new ductwork is a mixture of a main run of ductboard constructed on-site, two large flex returns (14" and 16") and the old metal branches re-wrapped. There are problems in all 3 areas.

The ductboard runs are basically OK, but two registers' ductboard boxes abut the main run, and the holes cut into the new run don't line up with the holes in the register boxes. No big deal.

The re-wrapping of the branch runs was poorly done, reulting a compressed wrap. In my case, the wrap was 2" initially, but the manufacturer allows 25% compression, so it should be 1 1/2" minimum, but I measure between 1/2" and 5/8" on all ducts. The manufacturer doesn't even have tables for R values for wraps with greater than 25% compression, but they estimate it's an R-2 (or so) wrap. To avoid condensation in my attic, the tables suggest R-7 or so; IECC requires R-8, and our local code requires R-6. I can fix that.

The long flexible return lines were not long enough, leaving inadequate duct to form the required 1/2 - D radius bends, so they just yanked it into place, kinking it. Even with all the yanking, they couldn't develop enough length to properly fasten the duct to the starter ring in the plenum box, so they just fastened the inner liner and left the insulation and outer jacket lying about 8" short.

My question is -- can I splice in a few feet of these large flex ducts to give me enough duct to work with? Do they make preformed metal collars to join the 2 lengths of duct? I think I'll need to go to a little-box store for supplies in any case.
 

Mikey

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Update... after spending some quality time in a little-box store, which thankfully sells to DIYers, but at (high) retail, I've got all my questions answered. Downside to the answers is it'll be expensive to fix: the correct ductwrap has to be special-ordered, the flex comes in 25' lengths, even if you only need 5', and correcting the various kinks will require rebuilding the return air transition on the air handler. But when finished, they're pretty sure my major problems -- condensation and consequent high attic humidity -- will be solved. As a (small) bonus, there will be a small improvement in airflow through the system.
 
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Terry

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Thanks for the update.
Sometimes when I get asked by a homeowner if something is possible.....the answer is always yes. It's just that some things take more time and money.
In this case, a box of duct that will be mainly unused, and more material and labor. But oh so worth it!
 

Mikey

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Worth it indeed. But I have to say, I'm really getting tired of following after so-called professionals to correct their sloppy, if not incompetent, if not (in this case) sub-code work. But there have been a few bright lights, so I'll keep trying. I'm getting too old for this.
 
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