For the record, 99-44/100ths of all residential forced air systems do not, repeat!, do not have an independently forced return. They are closed systems with what is best described as a "plenum" (central) return. Usually it is a large floor duct somewhere near the furnace. Essentially, it is the make-up air for the supply.

There is a great deal of bad information out there. Please DO try to verify any information from a reliable source before taking any irreversible action(s).

Peter Wieck
Melrose Park, PA