I am building a new 2080 sq. ft. ranch with a full basement (additional 2000 sq. ft. that will eventually be finished) and am wondering what size of unit I need. The new home will be in Ann Arbor, MI (Southern part of MI). The house has nothing "extra" as far as insulation, but will meet the new code requirements. It has 2x6 inch walls with cellulose insulation (R21) and blown in insulation in the attic (R49 I think). The windows are standard vinyl Pella windows. I haven't seen the load calculations, but one company quoted a ClimateMaster 3.5 ton and one quoted a Comfort Aire 5 ton. The house is on 10 acres, so I am going with horizontal trenches. I know I don't have a lot of details here, but it seems a big difference between the size of the system in the quotes. Could two companies really be this far off? What seems more reasonable? Thanks for any insight.