When we bought our home it had an old oil burner in a closet in the middle of the living room with no ducts or returns to the rest of the house (slab, 800 sq ft)...which was fine in 1954 when heating was cheap I guess. We have the old furnace replaced with a new one and had supplies added in the rooms through the attic. Just one 20x20 return in the living room wall and I cut dummmy registers in the walls between the rooms and shortened the doors a bit to allow air to move from the rooms. Heres my question: This little bitty house is dying for storage space...I was thinking of taking my upflow out and replacing it with a horizontal furnace in the attic. 1. the furnace is loud and we cannot watch tv without cranking the volume up 2. would like to gain the closet where the furnace is now What is the cost difference between a horizantal and a normal furnace? Would the return duct to the furnace need to be a 20x20 from the return? (thus removing the furnace but then filling it back up again with the duct work and eliminating any gained space) If I were to duct in returns in the rooms...Can I use the stud space or does it need to be lined?