I'm currently in the process of finishing our basement. Previously the builder had placed the cold air return in between the joists with the vent located in the ceiling of the basement center. As part of the basement reno, I'm dividing the basement into 2 rooms, so I need to move the cold air return so:
Each room has it's own return
Returns are located closer to the floor
I'm planning to extend from the existing return duct location and have it run to a stud cavity (sealed by drywall) in each room. To accomplish this, I plan on using rectangular ducts to extend over to the walls where the vents will be (about 5 ft). The rectangular duct will run perpendicular to the joists and will overlap where the original return was located in the joist cavity.
My questions are:
Is there a preferred method to transitioning from the joist cavity to a rectangular duct? How should this joint be sealed?
When running the duct to the stud cavity, I'm removing the top plate of the wall to insert the duct. How does this end get sealed?
Just take out that vent and extend it. If you have to drop below the joists to get it there, you may have to, otherwise, if both rooms are next to each other, place the vent in that wall, but do not use the same stud space for both rooms. Since the cold air return looks like it expands across two joist spaces, that will work for what you need.