The answer to 'how long will ductwork last' is that properly installed and maintained ductwork can last 10-25 years or more. The lifespan of your ductwork depends on factors like the material, climate, and how well it was installed and maintained. Metal ducts tend to last longer than flexible ducts, and ductwork in attics or crawl spaces may wear out faster than ducts inside the home's conditioned space.
Regular maintenance like cleaning, sealing air leaks, and inspecting for damage can help extend the life of your ductwork. It's a good idea to have your ducts inspected by a professional HVAC technician every 5-10 years to check for issues and make any necessary repairs.