Joist Panning(Lining) seems to still be popular. However, a have read in a few places that joist panning is difficult to seal and can pull air from unconditioned spaces. I am looking for an alternative to replace joist panning that is easier to seal and better all around.
So far the only option I have found was to use hard pipe. If I wanted to replace a joist panned return air duct with an equivalent hard pipe, what would be required?
Joist Cavity is roughly 14 1/2 in x 10 in. Stud cavity is roughly 3 1/4 in x 14 1/2 in. Now, I dont know if I can assume this, but isn't the air flow limited by the smallest opening? Could I assume, to be able to match this, I would just need to get as close to the stud cavity size as possible to retain similar air flow?
The closest hard pipe opening I found was this. http://www.menards.com/main/heating-cooling/ductwork/ductwork-fittings/3-1-4-x-12-x-6-stack-head-9-throat-each/p-1444432289493-c-14260.htm?tid=6704999512863625561 Which is 3 1/4 in x 12 in which is decently close to the stud cavity. I could then transition it to 7" round duct. Will this option be similar air flow as the panned version?