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Community and Q&A

Flex Duct for Range Hood Exhaust

drafthunter | Posted in General Questions on

Due to studs and Plumbing in the bulkhead above the range hood, I can’t fit solid duct in a straight line. Not even 4” solid duct.

What are my options? Whenever building code is mentioned, “smooth wall” and “air tight” are mentioned. I haven’t seen Rigid duct specifically mentioned.

So what about a smooth walled flex duct that also has high heat resistance? The run is about 2’ up, a 90 degree turn and then 6 feet to the outside.

I’m not worried bout performance as even with 4” flex, smoke is adequately removed with the fan on low and it’s an electric range. My main concern is potential fire hazard.

I was thinking about something like this:

Any help is appreciated

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  1. Expert Member
    BILL WICHERS | | #1

    That's not "smooth wall" as far as ducts go, it's a flex duct. The rough sides (compared to plain sheet metal) result in more flow restriction. You could use that stuff, it's just not ideal. If you absolutely have to use it, I'd use rigid duct as much as possible, and only use the minimum amount of flex duct in the areas you specifically need it. Note also that the rough surface of the flex duct is more prone to accumulating oil and dirt from a range hood, and will also be more difficult to clean.

    When I did my own hood install as part of a recent renovation project (I converted from one of the recirculating type hoods, which I don't like), I reframed part of the wall to allow me to run rectangular duct up between the studs into an attic space. I kept the run as straight as possible, and used rigid ducting the entire way, with just an adjustable angle fitting to make up for some misalignment between the stud wall and the rafters.


  2. Expert Member
    Akos | | #2

    I've run semi rigid aluminum (similar to dryer went stuff but larger diameter) for these before without issues. These tend to be significantly less restrictive than most flex ducts, not as smooth as hard pipe but close enough.

  3. AlexPoi | | #3

    Some semi rigid aluminum (not the cheap foil ones) ducts are fire rated to be used on a range hood. Like this one:

  4. drafthunter | | #4

    Thank you. I will try semi-rigid. Looks like it is ubiquitous for this use.

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