I own a split level and am in the process of finishing the laundry room. The furnace is in this room also, and the duct work is exposed below the upper floor joists. I want to resize the duct work to fit in between the floor joists to save ceiling height. The existing duct work is 6" X 19". I want to resize it to 8" x 141/2" to fit between the joists, then reattach to the existing 6" x 19" when it transitions down the wall at the far end of the room. Is this something I can do without causing any restrictions in the system?