Thanks for confirming the 8x12.
Yes, I've always thought the 6x30 was way undersized for a main duct, too. I actually hired a large local HVAC company to inspect the design a few years ago, and they said that everything was OK.
Someday, I may install AZEL dampers thoughout, and totally zone...
Thank you for your time,
I am converting a garage to living space, and would like to run ducts for heat/cool off my existing main duct. I could use some help in adequately sizing the ductwork. First, I'd like to state that my residential house heat/cool system is fairly standard issue, so if...