getting ready to finish approx 525 sq ft basment. I know furnace was sized to handle this additional space but now I need to run duct work for this new zone. Main room is 33 x 14.5. how many supply vents do i need ? and what size trunk line should I run off the plenum and how should I reduce down to connect each ceiling register. I know i will need zone dampers and a 2 zone control board for my furnace as well. I also planned on adding a new return air grill for the basement into the existing return air trunk line that returns the air from the first floor to the furnace. Any help on sizing duct work would be great. From my calculations it looks like I should supply with a 12" round and then from there somehow reduce down to supply each new register?