Performed the level 2 furnace cleaning. Burners and flame sensor are clean. Heat exchanger has rust and chipping. Unit did fail the smoke test, however, there were no cracks located and the combustion readings were normal. No CO detected in the air. Drain is clear. High limit passed the safety check. Heat rise was 47°. Unit is heating properly. When we return for the duct work, we will need to bring a 213 upgrade kit and filter.