I purchased a 3500 square ft home in Dyer, IN and I have a contractor ready to replace my 140 000 BTU furance with a Trane 104 500 BTU furnace. The old AC unit tonage is unknown and this guy recomends a 3.5 Ton unit and a 4 Ton coil with a 4 Ton fan. The house is a 2 story, 5 bedrooms, plaster, no insulation with a Mansard flat roof. Also have a 1200 Square ft addition with it's own HVAC unit. All brick for the house and addition. Partially shaded with mature trees. Does this sound right?