You can expect residential ductwork to last 25 to 70 years, with an average of 45 years. The big difference is due to the variables of materials, workmanship and maintenance. Flexible ducts, for example, will have a shorter lifespan than hard ducts. They also sink over time and restrict airflow if poorly suspended.
When flexible ducts are placed in accordance with the guidelines contained in the ACCA manuals on residential duct construction and HVAC installations, they are quiet, energy efficient and perform well, he said. 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 loss of energy due to friction inherent in the installation of flexible ducts, especially over longer stretches. Leaks in return air ducts can also have the opposite effect, as they draw unwanted air from a mezzanine or attic into the system. The industry group Air Duct Council, which claims to represent the manufacturers and suppliers of 95 percent of flexible ducts used in North America, said the product can last as long as a home's if install correctly.
New air ducts with appropriate seals and insulation can help prevent unwanted visitors from entering your home through the HVAC system.