I doubt any of us can make your decision for you. We need to know what is
the furnace make and model, the BTU's, how many existing runs, and how large
are the runs you're dealing with. How many elbows or corners and how long of
runs. It's all kinda complicated.
Since you are planning to put up a drywall ceiling, you might want to call
in a HVAC guy with experience in duct work, to get it right. Don't want to
have to tear out the ceiling to fix something later.
Or change the ceiling to 2 by 4 foot tiles. Drop ceiling.
Christopher A. Young
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