BDD - Back draft damper

BDD is a 2 inch deep back-draft damper (also known as a gravity louver) with light-weight damper blades. Nylon blade seals ensure a tight seal between blades and silent operation. It is ideal for pressure relief, intake, or exhaust in ducts, panel wall buildings, and doors. For controlling airflow in ducts or through wall openings, see VCD - volume control damper. Linked and counter-balanced design is available. BDD4 is a 4 inch deep version for use in self-framing walls or deep enclosures.

Dimensions and weight

2 inches (51mm) or 3.75 inches (95 mm)
Maximum 36 inches (914 mm) per panel; Larger vents made of multiple panels
Maximum 60 inches (1524 mm) per panel; Larger vents made of multiple panels
Approximately 2.0 lbs/sqft (9.6 kg/m2)

Width and height undersized by 1/4" to fit rough openings (unless otherwise specified).

Features and options


  • 0.070 inch (1.78 mm) thick aluminum extrusions
  • Blades move on 3/16 inch stainless steel pins in nylon bushings
  • Dual durometer nylon blade seals
  • Assembled with cadmium plated screws and rivets
  • Optional steel counter-weights for barometric operation
  • Optional linkage for coupled blade motion (aluminum angle and aluminum brackets)


  • 2" deep flange frame (1" flange) for exhaust applications
  • 2" deep channel frame for duct installation (optional)
  • 4" deep flange frame (1" flange) for deep enclosures (optional)
  • 4" deep channel frame for duct installation (optional)
  • Reverse flange (rear flange) frames for intake applications1 (optional)

Screen (optional; fastened on back face; not available on couter-balanced models)

  • 1/2" welded square mesh, 21ga galvanized steel (optional)
  • 1/4" welded square mesh, 25ga galvanized steel (optional)
  • 1/8" woven square mesh, 27ga galvanized steel (optional)
  • 1/16" nylon insect screen (optional)
  1. Hood (not supplied) or companion louver is recommended for intake applications.