My AC sales guy said such a contractor estimate formula, "one ton of cooling for every 400 sq ft" was common for tract homes, especially single level. My 1165 sqft home is in Las Vegas with 100-115 degree summer temps. He sold me a 3 ton unit, saying it can be upsized slightly, and that the 2 ton would have been to small for needs. Also since I wanted two-stage, there were no 1/2 sizes, so 3 ton unit was proper size. Does this sound wrong? No Manual J load calc done unfortunately, but may still have one done out of curiosity by another contractor since reading this forum.