How to install a backdraft damper

Updated February 21, 2017

Backdraught dampers allow air to move through a duct system when the air conditioning unit or exhaust system is pushing air. When the mechanical equipment is off, the damper closes to eliminate air from flowing back through the duct. Pressure and gravity control the functions of a backdraught damper, no motor or electricity is required for the damper to operate. Installing a backdraught damper correctly ensure the blades will open and close correctly.

Mark the mounting location of the backdraught damper on the inside of the duct work with a tape measure and permanent marker. Make one mark on the two vertical sides of the duct.

Align one side of a torpedo level with one of the marks. Adjust the level until the air bubble sits in the centre of the vertical bubble to show the level is plumb. Draw a line along the level with a permanent marker. Repeat the process to draw a line on the other side of the duct.

Slide the backdraught damper with the face of the damper blades facing with the airflow. Align the sides of the damper frame with the two level lines drawn inside the duct.

Run two No. 10 self-tapping screws through each side of the backdraught damper frame with a variable speed drill with 5/16-inch hex head adaptor. Keep the screws on the side of the frame furthest from the mounted damper blades.

Cut the end of a caulk tube with the nozzle cutter of a drop-in caulk gun. Secure the caulk in the caulk gun.

Apply a bead of caulk to the seam between the backdraught damper frame and the ductwork. Allow the caulk to cure for 24 hours before putting the duct in use.

Things You'll Need

  • Tape measure
  • Permanent marker
  • Torpedo level
  • No. 10 self-tapping screws
  • Variable speed drill with 7.5 mm (5/16 inch) hex head adaptor
  • Caulk
  • Drop-in caulk gun
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