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Bath fan duct routing vaulted ceiling

kevinjm4 | Posted in General Questions on

Do you run bath fan ducting up or down the ceiling rafters? (See picture attached) Also, I’m assuming you keep this run as short as possible to maximize r value in ceiling, correct?

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  1. user-6623302 | | #1

    Have you looked at roof mounted fans?

    1. kevinjm4 | | #2

      Haven’t heard of these no. Could consider.

    2. kevinjm4 | | #3

      Is this what is typically done/preferred in an application such as mine?

  2. Expert Member


    Of all the fan locations, inside a cathedral ceiling is the most problematic. It's very hard to insulate around the enclosure while maintaining both good R values, air-sealing and not interrupting ventilation. Is it not possible to wall mount it or even better to add a bulkhead?

    1. kevinjm4 | | #6

      Possible to mount on a wall yes, which would put it immediately over shower head. That is the only possible location if wall mounted. My fan says wall or ceiling mountable as well, however it seem awkward to have the duct connected to the side of the unit in a wall, seems ideal if it has the duct connection point coming out exactly opposite the grille.I’m sure it’s been done just seems awkward.

      1. Expert Member
        Akos | | #8

        Look at something like the Pansonic Whisper Thin, this can be mounted into a standard 2x4 wall.

        You can mount it on the interior wall that is perpendicular to the exterior and run the duct straight across the to the outside. There won't be much structure left of a 2x4 when you run ducts like this, so only works on non lead bearing walls. Add mending plates on either side as a bit of reinforcement and try to keep the fan close to the outside wall as possible.

  3. jamesboris | | #5

    I went through this a couple years back -- be sure to ask the manufacturer if it's even allowed to have your fan at an angle. Panasonic doesn't allow it as it interferes with the damper. There's a chance you could get away with it for a wall-mount fan. Probably best to go through the wall or do a service chase. If you do a service chase, I'd advise not trying to hide it... it won't work... better to accentuate it, make it a decorative thing with tile or something.

    1. Expert Member
      MALCOLM TAYLOR | | #7


      Exactly. Make it a feature.

  4. Expert Member
    NICK KEENAN | | #9

    Can you drop the ceiling in just the bath? Or wall mount it and run it out an exterior wall?

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