How to Install a Spiral Duct

Elizabeth Knoll

Spiral ductwork is common in commercial applications. It is widely used in rooms with "exposed ductwork." This is not concealed by a drywall or suspended ceiling. Because of the way spiral duct is made, larger ductwork is made with a lighter metal gauge. This allows a lighter duct that requires fewer hangers. The connectors have a rubber gasket that provides an airtight seal at each connection when you install it. This provides a connection that doesn't need to be sealed with duct sealer. You end up with a system that has a neater appearance.

  1. Measure the length of spiral duct needed, using a tape measure. Mark out a piece of spiral duct at this measurement around the entire circumference of the duct, using a marker.

  2. Place your reciprocating saw up to the mark on the duct and engage it. Apply pressure to cut into the duct. Once inside, follow the line around the entire duct with your saw. You should now have a length of duct at your measurement.

  3. Push the length of spiral duct on to the connector until it slides over approximately 2 inches. Notice that the rubber gasket completely disappears inside the spiral duct. This is providing an airtight seal at the seam.

  4. Screw the spiral duct to the connector with sheet metal screws and a cordless drill. Use one screw every 6 inches around the entire perimeter of the connection.

  5. Support the spiral duct from structural members at least every 8 feet, using spiral duct hangers and a hammer. Measure the distance between the support holes on the spiral duct hanger. Hang a threaded rod down from the structural member on each side of the spiral duct. The distance between the rods should be the measurement between the support holes. Slide the spiral duct hanger over each threaded rod and secure it with the appropriate size nuts and washers and a wrench set. Adjust as necessary to make your duct level.

  6. Install each successive piece of duct following this procedure until the entire system is finished.