Last year I had a fly by night guy install a/c in my home and now I am suffering for it. The ducts are a complete mess, but I cannot afford to have it professionally repaired right now. The AC unit is a 10 S.E.E.R. unit rated at 22,500 BTUH. My home is an old two-story house. There is a trunk line in the attic supplying 6 six-inch vents for the second floor. The evaporator, main supply trunk line, and 4 six-inch vents for the first floor are in the basement. There is 10 inch flex line connecting the trunk line in the basement to the trunk in the attic. The AC was set up with only 1 six-inch air return line and open vents on the return line trunk. I will be upgrading the returns, but I need some help in determining how much return air I’ll need. I am planning on using galvanized pipe for the returns if possible, but I’ll use box style ducting if necessary. Any suggestions will be greatly appreciated. Thanks!

Make sure you insulate all duct in attic.