I have one HVAC unit in the unfinished basement that is giving not enough cooling or heating upstairs (nothing in some places). Contractor suggsted upsizing the unit to 100K BTU from 80K BTU and 31/2 ton to 4 ton A/C. ALso, the ducting is not done right by the builder.

I thought of setting up zoning because we don't need cooling or heating same time upstairs and downstairs. But there are two trunk line going out from the unit (one on either side) that supply to first and seconf floor (all mixed up both sides, i.e, alternately feeding first and second floor). I would like to run two trunk lines on each side supplying first and second floor separately so that they can be controlled by dampers. Since the basement is unfinished, I thought this can be done easily.

Just upsizing furnace is $4K and system is $6K (no duct work)? I think it is too much. Quote for second unit in the attic (Heat pump and 2ton A/C is $6K)? My house is about 3200 sq ft and is only 5 years old.

Thanks for any suggestions and recommendations.