• In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to quiet a noisy forced-air system.


    1. Mark center of start collars on the return and supply side of the heating duct.
    2. Cut holes in sheetmetal ducts using a drill fitted with a circle-cutting jig.
    3. Attach start collars to duct with ¾-inch self-tapping sheetmetal screws.
    4. Install bypass damper between the two start collars; fasten damper with sheetmetal screws.
    5. Seal seams around start collars with foil tape.
    6. Adjust the counterbalance weight on bypass damper arm.
    7 Turn on furnace to ensure bypass damper opens.
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    • Difficulty: Moderate to hard
      This is a job best left to a heating professional

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      Video Directory

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      Tools List

      • drill
      • jigsaw
        Circle-cutting jig,
        used to cut round hole in metal ducts

      Shopping List

      1. Bypass damper

      2. 7-inch start collars

      3. ¾-inch sheetmetal screws

      4. Foil duct tape,
      used to seal seams in ductwork