Second opinion for client. Long time client at another address, first time here. Inspected both furnaces and found no issues with either system. One system is a zone system. Meaning more than one thermostat on one heater. Blower wheel is slightly dusted. System has utilized a 4 inch filter from the beginning. No carbon monoxide or gas leaks were detected while in attic. Both systems have adequate returns. The 80,000 BTU furnace has an 18 inch duct. Which will carry 1000 CFM. The other system has 1200 CFM. No additional ductwork is necessary as stated on clients previous contractor Milestones. Only recommendation I have today is a Reme Halo. $995.00