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New range hood with 8 inch exit,how many backdraft dampers needed.?

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  • New range hood with 8 inch exit,how many backdraft dampers needed.?

    Just bought a 30" range hood with an 8 inch exhaust,now trying to figure where and how many back-draft dampers I should use...I will be installing a new 8" roof vent,with damper and all 8 inch galvanized ducting will be insulated that goes through cold attic to the roof,maybe 16 feet total pipework.
    Would this one damper at the roof vent be enough,or should I add one closer to the hood's exhaust? Thanks,Huck50
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  • #2

    Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

    Ask your local building inspector or a local hvac guy.

    Codes vary by region.

    Nathan

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    • #3

      Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

      There is a damper at the roof vent and usually one at the hood. These are usually all that is needed. I don't recall any other dampers being needed according to code. Usually those are all that is required.
      Bill R. likes this.

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      • #4

        Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

        Originally posted by Greg from K/W View Post
        There is a damper at the roof vent and usually one at the hood. These are usually all that is needed. I don't recall any other dampers being needed according to code. Usually those are all that is required.
        Thanks,Huckfitty

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        • #5

          Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

          Trapping of warm moist air in a duct passing through an uninsulated space.

          That is an interesting question.

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          • #6

            Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

            Originally posted by bender View Post
            Trapping of warm moist air in a duct passing through an uninsulated space.

            That is an interesting question.
            This galvanized piping will be insulated where it goes through the cold attic to the roof...I think that is Ontario Building Code.Thanks,Huck50

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            • #7

              Re: New range hood with 8 inch exit,how many backdraft dampers needed.?

              Your right that is all that is required. The trapped air can still get out the seals around the dampers are only meant to keep wind from blowing back through the pipe into the living area. It will be fine. Its the way its been done since they started installing these fans. Just tape the joints with the metal tape. and do not use screws in the pipe.

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