I've got a 15-year old, 2-story walkout (3500 sq.ft.) brick home. It came with a 3.5 ton trane a/c and no upstairs a/c. (there's 1600 sq.ft up there!) As you would expect, it's always hard to cool the upstairs. Now, it's time to replace the original a/c and gas furnace. I'm leaning on getting a 4.0 ton Trane XL 16i heat pump and a Trane 90+ variable upflow gas furnace (have also looked at CarrierInfinity hybrid). Both dealers say that a single hybrid system will take care of the whole house, but I'm not convinced (based on what I've been able to read). I think I still need an upstairs unit (possibly another heat pump without strips, or an a/c). Obviously, $$$ don't grow on any tree I've got planted. So, what's a good plan of attack?