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vent bath fan through roof vents?

m2akita | Posted in Construction Techniques on September 8, 2009 06:16am

Working on a house where the previous owner installed exhaust fans in both of the 2nd floor bathrooms.  Unfortunately, they just connected the two fans to each other.  Basically, the fan from one bathroom is exhausting into the other bathroom.

Hip roof has two turbine roof vents.  Was thinking of just running the bath fan exhaust lines through the turbine vents instead of putting in their own dedicated vents.

Anyone see any problems with this?  The turbine vents are the only vents on the roof.  There are no soffit vents or any other type of intake vents ( most of the air is probably being drawn from the living space).  The attic is to be sealed off from the conditioned living space as much as possible. 

House is in central Virginia area.

Thanks for any input. 

Live by the sword, die by the sword….choose your sword wisely.
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Replies

  1. User avater
    Dinosaur | Sep 08, 2009 06:49am | #1

    If there are no intake vents, and you're gonna seal off the attic from the rest of the house, one turbine is gonna suck while the other blows. Or they're both gonna cavitate and do nothing useful. And which turbine does what will change, depending on prevailing wind on any given day.

    That being the case your proposal doesn't seem to me a good idea.

    Dinosaur

    How now, Mighty Sauron, that thou art not brought
    low by this? For thine evil pales before that which
    foolish men call Justice....

    1. User avater
      xxPaulCPxx | Sep 08, 2009 10:08am | #2

      I disagree. If he just piped it up so it terminated just below the turbine intake, he would be blowing air up into an exiting device that - depending on wind - might be sucking it out.Granted, it's not an airtight seal, but he's also not venting sewer gas either (even if it smells the same!)

      Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!

      Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

      1. DaveRicheson | Sep 08, 2009 01:22pm | #3

        I did that on my house years ago.

        Got condensation on the inside of the turbin  in the winter. Not bad. It took three years before I developed a small leak stain on the bathroom ceiling.

        I would cut the hole in the roof and install it properly.

        1. Piffin | Sep 08, 2009 01:31pm | #5

          Yeah, I saw one like that that had continuously damp sheathing around the roof vent because they had created a high humidity environment.Not as bad as others I've seen with mold growing everywhere within ten feet of the end of hose just laying loose in the attic. 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          1. DaveRicheson | Sep 08, 2009 01:58pm | #6

            Also ran one to a soffit vent many many years ago.

            Bad, bad, bad.

            Cost me more to fix that fudge up than  doing the roof pentration would have.

        2. User avater
          xxPaulCPxx | Sep 08, 2009 07:03pm | #8

          Ahhhhh!

          Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!

          Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

      2. Clewless1 | Sep 09, 2009 04:14pm | #13

        Ooh ... I must strongly disagree. In the Pac NW, we could never vent an exhaust fan w/out positive direct connection to the outside ... no laying the duct 'in the vicinity of an attic vent. He is NOT venting sewer gas ... but TONS of moisture!!

        Without a positive sealed direct connection, you have no idea if wind will blow that moisture right back into the attic.

  2. Piffin | Sep 08, 2009 01:29pm | #4

    with no soffit vents, those turbines are already compromised in effectiveness.

    So don't add to their load and reduce their air flow even further.

    besides, there is no way to connect to them in a way that assures that all the moisture laden air wil flow outside. Some will undoubtedly fall back into the attic.

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

  3. JTC1 | Sep 08, 2009 03:57pm | #7

    I would give each bathroom fan it's own roof jack and be done.

    Jim

    Never underestimate the value of a sharp pencil or good light.
  4. rdesigns | Sep 08, 2009 07:18pm | #9

    Without going into the turbine vent problem, which is another problem of its own, I recommend NOT venting the bath fans into the attic, even if they terminate close to the turbine vent.

    In winter, you would be creating condensation in the roof framing.

    Terminate the bath fans thru the roof or thru the soffit.

    When and if the attic venting gets fixed, the bath fans will already be done right, and, in the meantime, you will not have aggravated the problem with the improperly-vented attic that now exists.

  5. User avater
    rjw | Sep 08, 2009 10:37pm | #10

    It's very common in NW Ohio to nail off the bath fan duct just below a through roof vent. I've seen thousands with no sign of problems.

    Turbine vents are uncommon here; that might change things, although I'm not sure how.


    "Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

    Howard Thurman


    http://rjw-progressive.blogspot.com/

    1. fingersandtoes | Sep 08, 2009 11:03pm | #11

      I'm curious about what your code says about that. Ours won't allow it.

      1. User avater
        rjw | Sep 09, 2009 11:08pm | #16

        >>I'm curious about what your code says about that. Ours won't allow it.Code says don't do, the AHJs say it's ok.

        "Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

        Howard Thurmanhttp://rjw-progressive.blogspot.com/

  6. Jencar | Sep 08, 2009 11:10pm | #12

    I built a soffit in the bathroom, put a couple of recessed lights in there and the new bath fan.

    Ran the ductwork through the soffit and vented it to the outside with one of those covered clothes dryer flap thingies.

    Don't know if that's an option for you, but I'm always hesitant to cut a hole in the roof

  7. Clewless1 | Sep 09, 2009 04:18pm | #14

    Only if you direct connect and seal it. Not sure what will happen when the wind blows ... suck air through your exhaust fan and open the backdraft damper. May not want that, but maybe you don't care. If so ... eliminate the turbine and replace w/ vent cap w/ screen.

  8. berg | Sep 09, 2009 09:44pm | #15

    Best Option- Can those fans and install wall fans that vent directly to the outside and stay away from your attic envelope completely.
    'Cause you Will have probs venting to the attic!

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