2001 Lenox elite series 50K BTU 2-ton Upon arrival today and initial test running since the burning smell and smoke detector incident 4 days ago. The equipment turned on encycled like expected however after 10 to 15 minutes of run time the plenum temperature reached over 150° and the equipment short cycled on the primary limit that was recently replaced by a different company in February of 2024. Deep diagnosis and run testing with adjustments concludes that the heat exchanger energy transfer rate has diminished below the minimum standards of the furnace causing over 150° high efficiency exhaust temperatures with 25 PPM carbon monoxide and substandard efficiency burn rates in the high 80% range. All indicators of a worn out heat exchanger. Blower capacitor spec 5 UF running at 3 UF. Install new turbo 200 mini oval set to 440 volts at 5 UF System two 1998 Lennox 80% gas furnace under the kitchen appears to be running in fair to good condition with no additional run testing performed