Performed HomeCare routine maintenance inspection on 28 y/o Carrier furnace matched with 9 y/o Lennox AC that operates for whole house. Checked amp draws. Cleaned flame sensor. Cleared pressure switch tubing. Noticed gas line is flex entering furnace, which is incorrect. Should be hard pipe extended out of furnace. No water protection is present. System has poor combustion. Inspection determined compromised heat exchanger. Flame is rolling out of burner box. Significant rust throughout. Humidifier is inoperable. Recommend Apco Ultra for advanced air purification. Condenser electrical components are good. Coils are clean. Informed customer of all findings.