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Thread: Bathroom Exhaust Vent. Soffit -vs- Wall.

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    DoD Army bjferri's Avatar
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    Default Bathroom Exhaust Vent. Soffit -vs- Wall.

    I have a low profile 80 cfm Panasonic fan w/ an optional 3" vent adapter. Literature states going from 4" to 3" reduces cfm to 70, and increases .5 sones to .6. I'm okay with that...are there disadvantages to going 3”? Another thread someone posted stated vibrations. I haven’t installed it yet.

    My main question…my attic floor is open so I can run the vent to either the soffitt or would this cause moisture issues. I should be able to bypass the soffit and run it down the wall cavity and out the house., unless there's a 2x4in the way then I'm stuck. Which is best? I’ve never done this before and making holes in the house gives me a queasy stomach.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Running it down a wall cavity isn't very efficient (hot air rises). You might be able to run it out the wall under the sofit by just running down the bottom of the ceiling joist bay. But, so you don't fight the tendency of the hot air to rise, running it out a roof vent works better - probably a shorter run and works good. I'd run the 4" and forget the reducer. Panasonic is a good brand, so it probably wouldn't cause vibrations, but you might end up using a little more electricity, it'll be a little noisier (you may not notice), and it won't move as much air.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DoD Army bjferri's Avatar
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    Thanks, but I can't do the roof - if it were a first floor roof okay, but not a second floor pitched roof! Call me chicken. I'll try the wall under the soffit...or can I place the vent close to the attic fan that is nearby and let it out that way...if you think this is good practice? It may look odd. I don't like short cuts just to make things easier so I do want to do this right the first time and asthetics are important.

    Appreciate it!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It really should have its own outlet. Remeber, you are exhausting humid air (except for the occasional organic smells!), so you don't really want that in your attic. If it gets below freezing where you are, you could end up with frost on the inside of the roof, joists, etc...not a good situation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DoD Army bjferri's Avatar
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    Thanks again for the great advice! My thoughts exactly...well, except for the frost on the inside of the attic. That's a frightening scenario I never would have thought of!!
    Last edited by bjferri; 06-08-2007 at 03:49 AM.

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