I’ve noticed something a bit odd:

In my basement there are two “sets” of cold air returns that actually connect to the “main” cold air return on the furnace.

What’s a bit odd is that ONE of the sets actually “ties” into the other set at a diff. space in the basement.

Basically the house is a bit old, and what they did is nail some steel flashing (or whatever you call it) to cover the space between a floor joist set.  Then they attached a cold air return to that “duct” on the right side of the house and another “set” of return on the middle of the house (to the same “joist duct”).

I could possibly see that as making sense (the duct sets are 12″ ducts) as possibly providing two 12″ duct airflow volumes to the “main” return on the furnace.

But the middle duct STARTS out at 12″, then is reduced to 4 ” about 2 feet later, then continues to be 4″ for about 5′ and then goes back up to 12″ duct again.

What I was thinking of doing was making it ALL 12″ duct and then getting rid of the right-hand side duct set (while that duct set DOES attach to the “joist duct” that joist duct actually only services TWO air returns)

Any thoughts/advice?  I would prefer to do this now as I’m finishing the basement ceiling and want to “box” the ductwork with drywall and all that.

–Kevin