The answer to 'how much to replace air duct sealing' is that the cost can vary widely depending on several factors. Typically, the cost to replace air duct sealing in a home can range from a few hundred dollars to several thousand dollars, depending on the size of your home, the complexity of the ductwork, and the extent of the sealing required.
Some key factors that influence the cost include the materials used (mastic sealant, foil tape, etc.), the accessibility of the ductwork, and whether any ductwork needs to be replaced or repaired. Additionally, the cost will be affected by the labor rates in your local area and whether you hire a professional HVAC contractor or attempt a DIY project.