Hi All! My first post here, as I just found this forum this week. I'm a builder in Michigan and I'm breaking ground on a 4200 sf one story office building on Monday. My problem involves the bids I received for the HVAC work. One outfit insists that I will need 2 - 5 ton AC units and the other says all I need are 2 - 3 ton units. Does anybody have enough experience and/or a formula so that I can determine which one to go with? I'll be building on a slab, with 12' rough ceilings, dropped down to a 9' drop ceiling with all HVAC mechanicals in the 3' space above the finished ceiling. Ceiling will be blown in cellulose at r-46, similar walls to r-21. 24 - 4'x4' double glazed low-e windows and 3 exterior doors. Thanks!