How to Install a Spin-in Duct Fitting

By Robert Sylvus

A spin-in duct fitting connects a round duct to a rectangular duct. Many spin-in duct fittings contain damper blades. Technicians use the damper blades on spin-in duct fittings to balance the air flow through the entire duct system. Some spin-in duct fittings have extractor blades. An extractor blade increases the amount of air pulled out of the rectangular duct. Technicians often install spin-in duct fittings with extractor blades when the round duct must travel a long distance to reach its register.

List of Items Needed

  • Permanent marker
  • Rotary tool with metal cutting accessory
  • Safety glasses
  • Green-handled aviation snips
  • Duct-sealing mastic
  • 3-inch paint brush
  1. Hold the end of the spin-in duct fitting that connects to the round duct against the side of the rectangular duct. Trace the outside of the spin-in duct fitting on the rectangular duct, using a permanent marker. Set the spin-in duct fitting aside.

  2. Cut out the circular hole in the rectangular duct for the spin-in duct fitting using the rotary tool with a metal cutting accessory. Hold the rotary tool in both hands and follow the inside edge of the permanent marker's line with the metal cutting blade. Work slowly to avoid over cutting.

  3. Create a 1/2-inch-long notch on one side of the round hole in the rectangular duct, using green-handled aviation snips. The blades on the aviation snips lift one side of the notch, creating a space for the spin-in duct fitting's mounting slot.

  4. Align the groove on the spin-in duct fitting's mounting slot with the notch on the rectangular duct's round hole. Slip the groove over the notch.

  5. Turn the spin-in duct connecting clockwise. Work the groove around the hole in the rectangular duct one full revolution.

  6. Turn the spin-in duct fitting's extractor blade, if equipped, to the proper position. If the duct fitting uses an extractor blade, turn the duct fitting clockwise until the extractor blade rests on the downstream side of the rectangular duct.

  7. Cover the seam between the spin-in duct fitting and the rectangular duct with a duct-sealing mastic, using a 3-inch paint brush to spread the mastic.

Tips and Warnings

  • Wear safety glasses when cutting metal.

© Demand Media 2011