After very careful manual j, and finding out that with the burner and gas valve change that goodman does on their modulation furnace when converting to LP which makes for no derate, I can't decide which furnace to get. With different scenarios of "tight" or "average" infiltration and indoor temp at 70 or 67,(so 4 different scenarios) 60K makes the grade. If I add a 20% BTU need as a safety factor, then the 60K does not make the grade on 3 of them by between 2K and 9K.
Also, the house is cooled by a 3-ton unit, the 60K has a 3-ton blower, the 80K has a 5 ton blower.
Current furnace is a 81K output, and runs not even 6 hours during a 30 degree stretch over 24 hours.
what would you install in my house?