I have an old 2100 sf house with 11 foot ceilings in Atlanta GA. The current system that was there when I moved in, a Rheem 2.5 ton unit, doesn't come close to keeping the house cool in the summer.

The living room, dining room, kitchen and breakfast room are all on the west side of the house and there are no trees on that side, it pretty much bakes in the evening sun. There is not a lot of airflow thru the vents on that side of the house and there's only one vent per room to boot. When the outside temp hits the mid-90s, the temp in the west side of the house is in the low 80s.

There is actually good airflow thru the vents on the east side of the house, and it's fairly comfortable in either of the 2 bedrooms and the bath on that side.

I was wondering if adding another 2 or 2.5 ton unit, with maybe some additional ductwork, for the west side, and having the existing unit dedicated to the east side, would be practical.

The existing unit is around 10 years old, and will need to be replaced at some point, but it actually hasn't given any trouble and the air is still cold coming out the vents, there's just not enough of it coming into the house.

I'm going to look at getting more insulation in the attic, under the house, etc, but I'm pretty sure that's not going to cancel the fact that I don't seem to have adequate cooling. The question is whether to get one big, new unit for the entire house (along with some additional ductwork and vents), or go with dual units, getting a new smaller unit now, and eventually replacing the older unit when it fails.