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  1. #1
    Join Date
    Jul 2010
    Scarborough/Toronto, Ontario
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    spring-loaded backdraft damper keeps flapping


    We've just had a new range hood installed, vented straight out the back through an 8-inch diameter duct, with a new wall cap with spring-loaded backdraft damper.

    When it's the least bit windy out, the damper flaps and bangs. The sound is maddening, and the flapping allows cold air in (or warm house air out, maybe).

    Our electrician tried to increase the tension on the spring without affecting the damper's ability to open at the lowest fan speed. Yet it still flaps, and sometimes the damper just stays ajar now, and cold air really does pour out of the range hood into the kitchen.

    There's a critter screen on the bottom of the wall cap, so there can't be animals moving the damper.

    Why does the damper flap? Is it possibly the shape of the wall cap (triangular, not rounded on the top)?

    What can we do to prevent the flapping? Any ideas or suggestions?


  2. #2
    Join Date
    Aug 2000
    Central Oregon
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    Sounds like you have air migrating through your home. When the wind blows, the pressure in your home is fluxuating, when its high in the vent area it forces the damper open. When it's low the damper wouldn't move.
    Our house does it also and our micro vent bangs plus the water in the downstairs toilet moves around. from the pressure difference between the plumbing vent and sewer.
    I would say its another vent allowing infiltration. bath fan?
    If you think our goverment is screwed up. You haven't lived in another country.

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