It would seem that many posters have a similar issue with respect to getting the proper sized furnace. I have had eight contractors out for estimates and they are evenly split between installing an 80,000 and 100,000 btu furnace. They all swear they have done an analysis and theirs is the "right" size. I don't want to freeze here in central Indiana when it gets below zero. The old unit is a 25 year old 156,000 btu beast that is way oversized and cycles very frequently but keeps the house warm. The house is an 1800sf 1950's ranch with little insulation, large original aluminum windows, and a partially finished walk out basement. My gut tells me that an 80'000 unit will be mostly fine but may struggle some in a prolonged cold snap so I'm leaning towards the larger unit but get it in a two stage so it will be more quiet and efficient and still heat well during extreme cold. There is not much price difference in size but the 2 stage is definitely more costly. All the quotes were for a 92 to 95% efficiency. Am I off base here or should I be looking at something else? All the contractors did come up with the same 3 ton AC unit so I think I am OK there. Any help would be appreciated. Thanks.