Which furnace lasts the longest?

Which furnace lasts the longest based on average lifespan data and heavy-duty construction is Trane and American Standard gas furnaces that last 18 to 22 years on average with proper maintenance, longer than industry average of 15 to 20 years and longer than value brands like Goodman at 15 to 18 years. Trane furnaces like XC95m modulating and S9V2 two-stage variable speed are built with heavy-duty aluminized steel heat exchangers, thicker gauge cabinets, and robust components that are run tested at factory, contributing to longer life of 20 to 22 years with annual maintenance including filter changes every 2 to 3 months, burner cleaning, and heat exchanger inspection, versus average furnace at 15 to 20 years. Carrier Infinity 98 and Lennox SLP99V also last 18 to 22 years with similar heavy construction. Old furnaces from 1970s and 1980s with cast iron heat exchangers could last 30 to 40 years, but modern furnaces use thinner steel for efficiency, so 22 years is considered long today. Factors that make furnace last longest include annual maintenance, correct sizing via Manual J to avoid short cycling that causes thermal stress, keeping filter clean to prevent overheating that cracks heat exchanger, and moderate climate where furnace runs 3 to 4 months versus cold climate where runs 6 months, doubling wear. To maximize lifespan, change filter every 2 months, schedule annual tune-up at 100 to 150 dollars, and keep vents open for proper airflow of 400 CFM per ton.