Performed furnace clean tune x2; started with the work shop furnace removed and cleaned the burners along the flame sensor, inspected heat exchanger and did find heavy amounts of rust, checked gas pressures, and performed a combustion test verifying no CO in the airstream. I then cycled on the main furnace, removed and cleaned the burners along with the flame sensor, cycled the system and checked gas pressures, and again verified no CO in the airstream. These systems are currently operating but due to age and condition of the work shop furnace I highly recommend having annual maintenance done to ensure safe operations. Job complete