I am finishing my basement which is 330 sq ft. and surrounded by 3 walls of foundation and 1 wall that is the garage. I will be tapping into the existing AC unit for the supply vents, but was wondering about the need and placement for a return air vent.
Is one needed, and if so where should the placement be? The supply vents are going to be located in opposite corners of the ceiling.

Thanks!

If the air has no consistent means of returning to the existing return ( doors closed from basement) then yes it would be a good idea to install another return and it should be placed away from the supplys to draw the air through the room, opposing corner of room or between the new supplys. Mike