Seal Your Ducts

• 1). Reconnect all loose duct connections. Secure a round duct's inner liner to its collar with a duct strap, then pull the insulation and outer liner over the connection. Push the fiberboard duct seam together, then secure it with a stapler.
  
  
• 2). Clean the leaking area with a rag. The duct-sealing materials will not bond permanently to a dirty or oily duct.
  
  
• 3). Apply a layer of metal-backed duct tape to each leaking duct joint or tear in the outer liner. Press the duct tape onto the duct.
  
  
• 4). Cover the metal-backed duct tape with two layers of duct mesh. Cut the duct mesh to size with a knife. Press both layers of duct mesh against the duct's surface.
  
  
• 5). Apply a one-eighth-inch layer of duct-sealing mastic to the duct mesh with a brush. Extend the mastic one inch past all sides of the mesh. Use fiberglass-approved mastic, usually white, on flexible ducts, fibered duct board seams and duct insulation. Use sheet metal-approved mastic, usually gray, on sheet metal ducts.