This is an older forced air gas furnace by American Standard?? Model # GULA-100-2. There was no Serial Number. Input of 100,000 BTU and Output of 68,000. This is an oldie and I wonder if anyone has any idea of the age. My guess is in excess of 40. Sorry but I did not take a picture of the cabinet.
Just a guess my crystal ball was kinda foggy this morning but my guess age 30- 35 years I have only seen one 40 year gas forced air furnace that did not have a cracked heat exchanger. Tell it like it is unit has exceeded a average life expectancy for the type of equipment budget for replacement