Would like to field a duct size question if there is an expert out there.
I am splitting up a ceiling return air box. The original was two 12" flex hoses jammed into one box. I took one out. Replace the one return vent and place it in a 2' X 2' box.
Planning to take the other one a bit further to take up the return from another room.
Before I purchased another 12" hose, can I change the duct size up to
14" mid-run? I have a bag of 14" left by the original owner.thanks richard