As to your spacing question. In my home and what I've seen in others they are minimally spaced about 16" apart which coincidently is the floor joist spacing . And sometimes they are two takeoffs in the same joist bay (one going left, one going right). That said there is one feature of the trunk that somebody knowledgeable maybe designed, and that is that every so often (say 8 - 12') the trunk steps down a size. I beleive this is done to keep up pressure at the takeoffs closer to the furnace. So if you were creating a duct system from scratch a pro designer would be a good thing.
Wall cavities aren't always sealed. So you can pull in attic air.
Originally Posted by ace064
ACCA did do test on how much the position of a return makes. Minimal to no effect on comfort.
Originally Posted by wraujr
Remember, air is "pushed" into the return, not pulled.
Originally Posted by beenthere
I seem to remember seeing that documentation on this site as a matter of fact.
"Better tell the sandman to stay away, because we're gonna be workin on this one all night."
"Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."
"Just get it done son."
As I recall, it was Dash that posted it.
Originally Posted by hvacvegas
Yep, I agree and just that is recommended in manual D.
Originally Posted by timebuilder
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about duct location on the plenum.
in my climate (hot humid) putting the ducts too close
together, where the outer liners are in contact with each other
will cause condensation.
also if duct take offs are too close to each other it will be
a pita to properly mastic seal the take off, the inner liner
and then the insulation and outer jacket.
if the insulation and outer jacket are not in contact with the
plenum then the exposed duct take off will condensate.
as will all of it if not sealed.
mastics last. duct tapes fail.
I usually install a 4' plenum instead of a 3' just
to have the space around the ducts.
just my own experiences but I don't tap off end cap
or too close (within 18") of ahu/coil.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato