Opponauts- I'm in the process of getting my furnace (24 years old, runs rough, 100,000 BTU @ 80% eff) and AC unit (20 years old, 2.5 ton) replaced. I have had 4 estimates come in, and have received 2 estimates for an 80,000BTU @95% and 2 for 60,000BTU @95% . For the AC, I have received 1 estimate for a 3 ton SER13or16, 1 for a 2.5Ton of SER13or15, 1 estimate for 2ton SER13or16 and another wasn't in writing so i don't have it.

My question is, how do i determine which size to go with? All have stated they did a load calculation, but the one estimator (who also is giving the smaller sizes) is adamant that the others were using a rule of thumb over an actually ccalculation using the total number of registers, windows, insulation etc. Info on the house: 1.5 story brick ranch (1948 built, insulation on second floor, not sure on first), ~1400 square feet (not including basement), a good amount of sunlight, with 1 door, a sliding door, and 12 windows its in Pittsburgh, PA if that helps anyone. It does have a 1 car garage (OPPO Related). Any help would be appreciated.

A10 for your troubles: