How to Install an Insulated Flexible Duct

For buildings that use a forced-air heating and air conditioning system, ductwork is an essential part of that system. One type of duct used in these systems is insulated flexible duct. This type of duct consists of a metal wire coil wrapped in insulation, with flexible plastic encasing the coil and insulation. The flexibility of the ducts allows for easier installation when working around other objects, but the flexible ducts must be properly supported for them to function correctly.

Connecting to Sheet Metal

Flexible ducts can often be found in forced-air HVAC systems.

Measure and mark the needed length of the duct.

Cut through the plastic and insulation of the duct with a utility knife or scissors.

Cut the wire with wire cutters and pull back the plastic and insulation.

Slide at least 1 inch of the center of the flexible duct over the hole on the sheet metal duct. Wrap two layers of duct tape over the joint to seal it, then place a hose clamp over the joint and tighten it.

Pull the plastic and insulation back over the wire core and secure it with two wraps of duct tape.

Splicing to Flexible Duct

Fold back the plastic and insulation on two pieces of flexible duct.

Connect the two pieces of flexible duct with a 4-inch metal sleeve.

Wrap duct tape twice around the spot where the ducts connect.

Place a hose clamp on each duct where it comes into contact with the metal sleeve and tighten the hose clamps.

Pull the plastic and insulation back over the wire core and cover the seam with duct tape, making two passes.

Things You Will Need

  • Tape measure
  • Utility knife or scissors
  • Wire cutters
  • Duct tape
  • Hose clamp
  • Screwdriver
  • 4-inch metal sleeve


  • Allow the flexible ducts to run for no more than 5 feet without being supported by a ceiling joist or hangers.
  • Handle the duct carefully so you don't tear it.
  • Avoid bending the ducts around sharp corners.

About the Author

Carson Barrett began writing professionally in 2009. He has been published on various websites. Barrett is currently attending Bucks County Community College, pursuing a Bachelor of Arts in sports management.

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