I am tearing down walls to remodel my kitchen but one wall has a return air duct near the ceiling (no actual ducting in the wall, it's hollow between the studs.) There is only one other return air duct in the area (about ten feet away) but the room will be very open once the walls come down. There will be no interior walls left so my only foreseeable option is the floor. Can I have return air duct on the floor? Also there are cathedral ceilings in the area; no attic.