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  1. #11
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    Default Re: Venting a bathroom exhaust fan

    SherryH ... classic example of an incorrect roof vent install.

    Ideally the duct should be attached to the exhaust hood ( and sealed at the connection ) then inserted from the top side of the roof sheathing and the interior ducting continue on from there. Instead in your case it was installed with the interior ducting stopping at the underside of the roof sheathing and relying on the exhaust hood insert to somehow magically seal itself.

  2. #12
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    Question Re: Venting a bathroom ehaust fan

    Quote: "Remember you want to go out and away as you go up (i.e. not just straight up but slightly out towards the perimeter) as you direct your venting."

    Dwarfwytch-- why not straight up??

  3. #13
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    Question Re: Venting a bathroom ehaust fan

    Also, Dwarfwytch--

    You wrote: "A hood proud should take care of any issues." What is a roof proud? Or was it just a typo?

  4. #14
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    Question Re: Venting a bathroom ehaust fan

    Dwarfwytch,

    I understand your diagram, but unfortunately it doesn't fit my situation. My fan's duct opening is on the side of the fan (not the top), so the duct at that point must be horizontal. There isn't room to run the horizontal section toward the eave, so I was planning to run it the opposite direction for 3-4 feet, then turn it 90 degrees straight up through the roof. I would use a roof vent hood as you suggest.

    To run the vertical at an angle as you suggest would require either a bend that's sharper than 90 degrees or an extended horizontal run across the centerline of the house. Both seem less efficient than what I was planning to do.

    What do you think?

  5. #15
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    Default Re: Venting a bathroom ehaust fan

    Unfasten and turn/rotate your fan unit in the ceiling so that you can connect using only one elbow (right at the fan unit)......if at all possible. Each 90 degree elbow is equal to 10' of straight run. You want as few elbows as possible to maintain good air flow.

    If attaching the elbow directly to the fan unit means that a problem is created because the exhaust piping will line up with (or too close to) a roof rafter or truss, then add a short length of straight pipe to the fan unit before mounting the elbow....so you end up between the rafters or trusses.

    Locate the exact position of the vent-hood in the roof VERY carefully or your pipe won't line up right. (If that happens, your project will get complicated and probably very frustrating.) Measure and then assemble (or cut) the longest piece of the vent pipe that will fit between the elbow and the roof deck and use that to locate the right spot to cut the vent-hood hole. (The solid blue part of the pic is an integral part of the roof hood. Your pipe must align nicely with that when all is said and done)

    If you can't make the rigid pipe work, then buy some aluminum flex pipe and use that. (But don't buy the plastic vent tubing)

    Use aluminum foil tape on all the joints/seams.

    Don't forget to well-insulate whatever piping you use.

    Make certain you know how to properly mount the vent-hood as regards the shingles (or whatever material comprises your roofing) or you'll have a leak. Black goop and/or caulk is not a long-term viable substitute for proper installation.

    Run the fan unit for the entire time you are showering or bathing and for 10 minutes minimum after you shut off the shower/drain the tub/leave the bathroom. Install a timer-switch in place of the toggle switch if returning to shut off the fan is too much hassle.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by goldhiller; 09-05-2007 at 10:59 AM.

  6. #16
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    Aug 2007
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    Default Re: Venting a bathroom ehaust fan

    Thanks for your input, and sorry for the confusion---I don't have software for drawing diagrams. I planned to position the fan vent toward the interior, and run the duct from it 4' horizontally, then 90 degrees vertically up through the roof. In other words, the duct would be a simple right angle 'L' shape. On your diagram view, the 'L' would attach to the left side of the fan.

    I read a fan installation guide that emphasized the need to go at least 4' horizontally before making any bends. It didn't give a rationale, but I thought I should follow that advice. But I gather you don't think that's necessary??

    If I understand it, DwarfWytch's concern with straight vertical duct is that it exits at an acute angle to the roof plane and may cause condensation problems. Couldn't I solve this by bending the top of my 'L' rightward near the roof, so that it exits at a 90 degree angle to the roof plane?

    I have considered a remote inline fan, but haven't found any as quiet as the new Panasonic model (.6 sones measured at the ceiling vent).

  7. #17
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    Default Re: Venting a bathroom ehaust fan

    jray,

    I'd say go ahead and toss in that 4' horizontal run if you like. I've never had a problem resulting from installing without it though. So long as the pipe is well-insulated and you run the fan for 10 minutes or so "after the fact", there really shouldn't be any condensation issues......or at least I've never had any with my installs. I have seen many problems from condensation dripping back down the line and even large lumps of ice in the line when no insulation was used in cold climates.

    Yes, if I understand correctly....you can toss in another ell up at the top of the pipe to get your alignment and connection to the roof hood. As a matter of fact, you're gonna need it to get connected if you've got a straight up/plumb pipe as it approaches the roof deck. Remember these ells are very adjustable and can be twisted to any angle from 90 to 0 degrees....so you should be able to acquire whatever angle you need. Can get frustrating sometimes though as it's kinda like playing with Rubik's Cube. <G> Trial fit all of the pipe run including that last ell at the top before you determine where to cut the hole in the roof deck.

    PS- If you're running a Windows-based OS, you don't need any special software to make simple drawings. MS Word or Paint will do that. I drew that with Word in about 60 seconds and then used Wisdom-soft Screenhunter (free download) to lasso the part of the page that contained the drawing. (Use the rectangle choice which allows you to lasso a specific area of the screen) Screen hunter will automatically save that file to whatever folder you create/desire for caching. Then you just direct the attachment facility here to that file to upload it. If you're looking for a piece of software to do more complex drawings.....try Google Sketchup. It's also free and is richly featured.
    Last edited by goldhiller; 09-07-2007 at 11:23 PM.

  8. #18
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    Default Re: Venting a bathroom exhaust fan

    jray... I had just installed a NuTone IFL120 in-line fan which I found somewhat easier to install than conventional ones. It's pretty quiet even with the fan only three feet away from the vent opening in the bathroom , a slight dull drone. The further the fan is away from the interior vent opening generally the quieter they will be.


    notice the gentle bend instead of a sharp 90 degree.








    That's the only thing that's seen and because everything is plaster this made installation a breeze with minimul damage to the plaster to fix.




    Not to beat this topic to death ... but here are some links to some information :

    http://www.nutone.com/product-detail...roductID=10330

    http://http://joneakes.com/cgi-bin/getdetailscals.cgi?id=1979

    http://joneakes.com/cgi-bin/getdetailscals.cgi?id=1756

    http://joneakes.com/cgi-bin/getdetailscals.cgi?id=1733

    http://joneakes.com/cgi-bin/getdetailscals.cgi?id=1307
    Last edited by canuk; 11-23-2007 at 09:43 PM.

  9. #19
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    Aug 2007
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    Default Re: Venting a bathroom ehaust fan

    Everyone, thanks for taking the time to respond. You've given me great information, and I think I have everything I need now.

  10. #20
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    Default Re: Venting a bathroom ehaust fan

    canuk,

    Sweet!

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