I'm looking at getting a 90%+ Trane gas furnace to replace a 30 plus year old American Standard unit. The old furnance is 55% AFUE, and is a 120,000 BTU. The house is 1350 square feet on 2 levels but there is only 1 register on the second level and it gets warm enough from rising heat. Insulation is average (brick veneer, nothing in the walls), pretty typical for a 60 year old house.
The new furnace will work hand in hand with a 5 year old 3 ton Trane central a/c unit. The contractors have given me estimates for both a 60,000 BTU furnance and an 80,000. Is there a good way to determine which is more appropriate for the system? I am told that either one has enough fan power to push the a/c in the warm weather, but I'm concerned about the furnance running too much or not enough depending on the size.
Thanks in advance.