The lifespan of duct sealing can vary depending on various factors, including the type of sealant used, the condition of the ductwork, and the level of use of the HVAC system. Generally, well-executed duct sealing can last several years. Some manufacturers claim their sealants can last up to 10 years or more. However, it's important to note that duct sealing is not a permanent solution. The sealant can degrade over time, and the ductwork can shift or develop new leaks. If your ducts are leaking or you notice an efficiency decrease in your HVAC system, consult a professional to determine if duct sealing or other repairs are needed.