Need to replace broken 2.5 ton central air unit. It cools about 1400 square feet. Old unit is over 20 years old. We're in process of improving insulation and have had received a number of quotes for new units, although most want to install a 3 ton unit or another 2.5 ton unit. No one is willing to perform a manual J load calculation. We are looking to take advantage of tax rebates etc, so are looking for energy efficient models. We live in Baton Rouge, Louisiana and need help figuring out which brand to use, size of unit etc. Any advice?