How to Connect a Flexible Duct

Written by william misch
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How to Connect a Flexible Duct
Flexible duct is more versatile and easier to install than metal duct. (Thinkstock/Comstock/Getty Images)

Flexible duct has become the most common type of duct used on new installations. While it may not be as durable as metal duct work, flexible duct is faster, easier and more versatile to install. If installed properly, flexible duct is efficient and long lasting. The key to installation is sealing the duct connections to the trunk line and register boots properly, and hanging the duct work appropriately.

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Things you need

  • Flexible duct
  • Mastic adhesive
  • Nylon strap
  • Strap-gun

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  1. 1

    Measure the length of the duct from the collar on the trunk line where the duct will tap off to the register boot where the air is delivered. Allow 2 inches on each end of the duct to slide onto the collar connector and the boot connector.

  2. 2

    Stretch the flexible duct out and measure the proper length. Cut the outer cover and insulation of the duct with a razor knife, and cut the support wire with wire cutters.

  3. 3

    Lay the duct out where it will be installed. Coat the collar connector that taps off of the main trunk with mastic adhesive, and slide the inner liner of the flexible duct onto the mastic. Secure with a nylon strap tightened with a strap gun. Slide the insulation and outer cover over the inner liner, and secure with a nylon strap.

  4. 4

    Strap the duct up at least every 5 feet if the duct is to be suspended, as in a crawl space. When running the duct, do not make any sharp turns that will kink the duct work or cause a restriction to air flow. Connect the far end to the boot connector. As with the collar, coat the connector with mastic, slide the inner-liner over the mastic, and secure with a nylon strap. Pull the insulation and outer cover over the inner-liner and secure with a nylon strap.

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