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How to Install a Duct Wall Cap on Aluminum Siding

Duct wall caps provide a finished, waterproof look to venting that terminates on the outside of your home. Common ductwork that ends on the side of the house includes dryer vents and exhaust fan ductwork. To terminate ductwork on the outside of aluminum siding, orient the hole in a location that can be weatherproofed properly. For aluminum and vinyl siding, mounting blocks that match the profile of the siding allow a clean look that can be weatherproofed.

  1. Measure the area to determine the duct wall cap's location, using a tape measure. Mark out the center of the hole for the duct you wish to penetrate the aluminum siding.
  2. Drill a hole 1/4 inch larger than the duct diameter with your hole saw. Common ducts for exhausting are 4 inches, so you would drill a 4 1/4-inch hole.
  3. Trim the edges of the mounting block to fit the exact profile of your siding with your hacksaw. Level the mounting block and screw it to your siding with the provided screws.
  4. Slide the pipe stub of your wall cap through the hole on the mounting block. Continue to slide the pipe into the hole until the wall cap is flush with the mounting block.
  5. Screw the wall cap to the mounting block with the provided screws. Caulk around the perimeter of both the mounting block and the cap to make the penetration watertight, using silicone caulk and a caulk gun.

Things You Will Need

  • Tape measure
  • Drill
  • 4 1/4-inch hole saw
  • Mounting block
  • Hacksaw
  • Level
  • Silicone caulk
  • Caulk gun

Warning

  • Screwing the wall cap directly to the aluminum siding will likely leave large gaps that will be prone to leaking. Always use a mounting block.