When it comes to residential ductwork, you can expect it to last anywhere from 25 to 70 years, with an average of 45 years. The difference in lifespan is largely due to the materials used, the quality of workmanship, and the level of maintenance.
Flexible ducts, for instance, will have a shorter lifespan than hard ducts. If not properly suspended, they can also sink over time and restrict airflow.
Leaks in return air ducts can have the opposite effect, as they draw unwanted air from a mezzanine or attic into the system. The Air Duct Council, which claims to represent 95 percent of flexible ducts used in North America, states that these products can last as long as a home's if installed correctly. When flexible ducts are placed in accordance with the guidelines outlined in the ACCA manuals on residential duct construction and HVAC installations, they are energy efficient and work well. The International Association of Plumbing and Mechanical Officials is considering limiting the use of flexible ductwork in residential projects to no more than 5 feet in length due to the energy loss caused by friction when installing flexible ducting, especially for longer stretches.
Installing new air ducts with appropriate seals and insulation can help prevent unwanted visitors from entering your home through the HVAC system.