Today we came out for front building not heating 1997 Lennox 100k furnace with matching 4 ton ac r22. Inspected complete system found failed thermostat in front hallway lobby. Bypassed thermostat and inspected system found draft inducer motor over amping. Motor could fail at anytime, inspected heat exchanger found severe metal fatigue and hot spots due to furnace almost being 30 years old. Flame rollout switches and fuel rail are severely rusted out and could fail at anytime. Due to condition of equipment and age need to update. Performed band aid option installed new thermostat for temporary heating. Scheduled install supervisor to give options on updating equipment. Left equipment operational although it could fail at anytime there is no warranty on repairs made today