Question:
I am shopping around for a central air conditioner that will be installed in
our 850 sq. ft home... any advice?
Answer:
Get the best installer you and find. Then the highest seer that you can
afford.
Try this site for comparisons.
http://198.147.238.24/ac_calc/default.asp
Granted you do not have an system now but you can look at cost/savings
pretty easily.
Attic insulation is always a good idea and pretty reasonable compared to
some of the other things a home needs.