What would be recommended? I am gutting my upstairs. Two-story house that was built with gravity central heat converted to forced air with no changes in ductwork. My main question is should I install return air ducts in the upstairs if possible. I have supply ducts in each room upstairs but no returns. I can measure and give furnace and air info at a later date. Thanks for the help. Chuck
Does the home still have floor grills open between floors from the original gravity heating system? If so, and you are going to leave them then I'd say you should have enough return air getting back to the unit.
Otherwise, how much space is there under the doors upstairs, and do you have an open hallway?
Returns upstairs placed high on the interior walls or in the ceiling will give you the best comfort for cooling. Don't know if you have AC or not but now's the time to plan for it unless you live where it's never going to be needed.