20 years ago, we had a 3.5 ton forced air/central ac system plus ductwork installed in our 3-story (2 floors, finished attic, cellar), drafty 1920s home. Several air returns were included on the 1st floor, none on the 3rd floor (only 1 heat/ac duct; living space ~ 4800 cu ft) and 1 in the central hallway of the 2nd floor.

2nd floor = 5 heat/ac vents (1 in each room) ~7000 cu ft of living space. To create the return, the house's old laundry chute was closed off via basement ductwork, and a vent was cut into its side on the 2nd flr. The vent sets about floor level at the top of the stairway going down to the 1st floor.

A proposed kitchen remodel would completely knock out the old laundry chute at ground level, leaving no functioning cold air return for the 2nd floor.

My question is this: currently, my stairway functions as cold air return for my 3rd floor. Could the 2nd floor stairway serve that same purpose (or is this a flawed design)?

In my living room there is a cold air return directly below 2 bedroom doors on the 2nd floor hallway. Should I expand that duct up to the 2nd floor to serve as cold air return for both floors?

Thank you for your advice.

PS - about 4 years ago I replaced the furnace with a high-efficiency 2-tiered (?) forced air system, same size as original (so now I have a basement full of pvc pipe and an unused chimney). No ductwork changes were made at that time.