The answer to 'how often to replace air duct sealing' is that you should generally replace air duct sealing every 5-10 years, depending on the condition of the existing sealing. Air duct sealing helps prevent leaks and improve the efficiency of your HVAC system, so it's important to keep it in good shape. Over time, the sealing can dry out, crack, or become less effective, so it's a good idea to inspect it regularly and replace it when needed.
The lifespan of air duct sealing can vary depending on factors like the quality of the original installation, the climate, and how much stress the ducts are under. Homes in hot, dry climates may need more frequent sealing replacements than those in more moderate areas. Additionally, if you've had any major HVAC work done that required opening up the ducts, you'll want to check the sealing and replace it if needed.