Happy July 4th! I have an older Heil Cabinet style A/C unit, split with an 80+ Bryant furnace. I have two return air sides for this set up, both at the top of the wall. One is in the living room, the other is in the hallway. the supply ducts are in the floor. The filter size is 16x24x1, both of the returns are pretty close to this size. My question is this, do I need to use both return air sides, or is one efficient enough? My house is around 1,460 sq.ft.