New system

[mcot]

I have a 30yr old furnace in my house no AC. I figure it is time to replace. Furnace replacement is no problem AC is. I have a 2400 SF tri-level (out side measurements). I have 2 returns one on the upper level and one on the midlevel which is not enough for a 3.5 ton AC. The suggestion has been made of putting another return high on the stairs leading from the lower level to a partially finished basement. Does this sound workable or will I be creating a negative pressure in in the basement?

The equipment I am leaning towards is an Amana 96% variable speed and a 14 seer AC. What do you think?

[dash]

If the basement is conditioned and the return is sized correctly,no problem as far as the return side.

Adding the PD(Pressure drop) of an A/C coil to the supply side,you may have a problem with the sizing of the supply ducts,that should be addressed before installing.