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Thread: Can I vent my exhaust fan into a joist bay?? No moisture...

  1. #16
    Plumber Cass's Avatar
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    He should still install a fan. No one opens the window in the winter...... that is unless the wallpaper starts to peel.

  2. #17
    DIY Senior Member sulconst2's Avatar
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    here's a thought. how about doing a wall mount fan and dropping the exhaust down to the basement then out the back?

  3. #18
    DIY Senior Member lithnights's Avatar
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    Quote Originally Posted by sulconst2
    here's a thought. how about doing a wall mount fan and dropping the exhaust down to the basement then out the back?
    Good idea. I was actually thinking of doing something like that....

    The only snag I thought of is that the 1/2 bath is in the middle of the house and I'd have to run the duct ~5 feet down to the basement and then about 16 feet of duct across the basement to get it outside. Not ideal but definitely doable. Not sure if 20+ feet is OK for a duct run..

    But it's better than running it 12 feet to the front of the house and exiting through the soffit on top of my front porch. Not exactly aesthetically pleasing..

  4. #19

    Default dead end vent in joist bay

    Something to consider: while an exiting vent pushes air outside, without pressurizing the joist bay space, a short hose pushing air into entire joist bay space from first floor might act as a worse 'chimney' in the event of a fire, possibly spreading the fire itself, if not harmful smoke and toxins.

    I don't know if this is expressed in the code specifically, but it may be one reason its not allowed.

    I wouldn't do it. Insurance company would probably use it to limit coverage if it were discovered after a house fire, as a contributing factor to spread of fire to 2nd story? Just a guess on my part.................I think that's why a few places require bath fan housings to be caulked or sealed to drywall ceiling.

  5. #20
    Electrician, JIW sparking5's Avatar
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    Brainstormin' here:

    1. Febreeze & radio

    2. Scented Candle & chanting

    3. Perfume & wind chimes (manually moved)

    4. Fresh baked brownies & box fan


  6. #21

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    Fresh baked brownies to mask the aroma of 'fresh baked brownies'. Geniously ironic!

  7. #22
    DIY Junior Member alwaysremodeling's Avatar
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    If anyone uses the sink in the bathroom and uses the hot water say for shaving then they are putting moisture into the air. If you vent this moisture into your rafters you will have a bigger problem then the aroma from someone doing #2 in the toilet. I would say definately find a way to get that air outside the home. Here in the NW mold and mildew are very big problems and most of the time it is from faulty venting from the bathrooms.
    Someday this house will be a home!

  8. #23
    DIY Senior Member lithnights's Avatar
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    The candles and the "fresh baked brownies" are interesting ideas. I will keep them in mind. ; )

    Regarding the shaving comment, this bathroom will likely never have that occur since it is the 3rd bath in the house. I do see concern with the hot water and the resulting moisture, but that will likely happen once in 10 years. You never know but the chances are against it.

    Our current downstairs bathroom (which this new bath is replacing) has never had the hot water run for more than 20 seconds at a time. It's just hard to see that little bit of running water causing mold problems but I guess it could.

    I am still trying to figure out a way to get it vented out of the house... it's just such a long run...

  9. #24
    Homeowner geniescience's Avatar
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    Default If not humidity (moisture), then pressurized air is the problem.

    OK, ok, I get the picture. But first I will say something about moist air.

    You breathe, you expel moist air. Have you ever been in a cow barn in the wintertime? Is it moist in there! We breathe too. If nobody is going to spend much time in this bathroom, then your regular ambient air moisture is all you'll have to deal with. Granted.

    Now, on to problem number Two. A balloon can only be blown up a certain size before it pops. Your wall cavity won't pop, but you will be running a fan to build up pressure inside a cavity. It is a hole, a container, a space, that you want to receive air into. Either the chosen cavity is airtight or it is leaky. In one case, you will be running a fan against a buildup (air pressure buildup) which will cause the fan to simply maintain a head of pressure and not move anymore air at all after only seconds, not minutes. Not what you want at all. Air can only be compressed so far before it becomes a massive obstacle. Air is not infinitely compressible. Not at all.

    In the other case, you will be sending air into more places than you appear to be planning for, because it will leak forward throughout everywhere it can. Dusty, inter-joist, dirty air, getting swirled around by fresh bathroom air, leaking out of switchplates and electrical plugs and door frames and Who Knows Where Else. -- Aghh... Disgusting. Hope this is clear. The dust left over from the initial construction is best left undisturbed. My opinion.

    David

  10. #25
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    Let me preface this by saying I am not a professional like many of these guys. My knowledge and experience comes from renovating/remodeling 80+ yr old homes -- our own home(s) as well as friend's and family's homes. I've never been paid for this kind of work, but I'm not a fool and learn how to do things before jumping in.

    As you already know, the preferred method (rather the 'required' method by code) is to vent to the outside. Several have already pointed out the risks of moisture entering into the cavity between your joists. Based on your initial post I assume that you already recognized those concerns. Only you can be the judge of how much moisture may be vented into the cavity and how often it might occur. Based on your comments, I would not view moisture as a likely potential problem -- possible? Yes. Likely? Probably not assuming the facts that you present. Incidental humidity created from one's breathing or a running sink faucet are highly unlikely to be problematic for you unless the 1/2 bath is EXTREMELY small. I typically-sized half bath is going to have sufficient air volume that the humidity created by normal handwashing, flushing, breathing will be negligible, IMO and experience. Now, if someone runs the faucet with steaming hot water for a healthy length of time, then, yes, excess moisture could (probably would) be created in an amount sufficient to cause a problem. However, if you or someone else accidentally vented that moist air into the cavity you could simply leave the fan on for an hour or so and the moving air within the cavity should be sufficient to lower the humidity of the initial moist, vented air and prevent any problems, particularly if the cavity between the joists is of fairly good size. (It should probably be noted that I am assuming that there is no insulation inside the joist cavity -- if there is insulation I would not vent into it no matter what as it is just too easy for problems to develop.)

    The only real concern I would have, if I were in your shoes, is nelie's comments about fire safety. Although it's not likely that your house would ever be involved in a fire, it is possible that the vent could contribute to smoke/fire damage if such occured. I would not be concerned about the possibility of denied coverage though -- failure to follow code by the homeowner is not a valid basis for denial of coverage, at least it's not under Missouri law where I live. Nelie's point is well taken though.

    Ultimately, it is your house and you have to assess the risk/reward of venting or not venting. I can tell you that I have seen a fair number of incorrectly vented fans in these old houses and have yet to see a problem as a result. I wouldn't foresee a problem based on your description, but there are no guarantees.

    If you do decide to vent into the cavity, I would just be diligent about running the fan longer than normal -- the increased and sustained air flow within the cavity will help prevent any problems with regard to moisture.

    Hope that helps -- take it FWIW -- which isn't much considering the cost for the advice. :>)

    good luck, let us know what you decide to do.

  11. #26
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    David brings up an excellent point. This should be a real consideration in your decision, IMO.

    If it's not too much trouble, I don't see a problem with venting it to the soffit over your porch. Soffits often have vents so I don't think it would be viewed as aestheically offensive. The only possible problem would be if the vent is right over the porch swing and someone drops a bomb while the rest of the clan is happily swinging outside. There is probably enough wind and air dispersion that it won't be a problem, even then, 90% of the time. Besides what are the odds that someone will turn on the fan while others are under the soffit vent on the porch?

    Quote Originally Posted by geniescience

    Now, on to problem number Two. A balloon can only be blown up a certain size before it pops. Your wall cavity won't pop, but you will be running a fan to build up pressure inside a cavity. It is a hole, a container, a space, that you want to receive air into. Either the chosen cavity is airtight or it is leaky. In one case, you will be running a fan against a buildup (air pressure buildup) which will cause the fan to simply maintain a head of pressure and not move anymore air at all after only seconds, not minutes. Not what you want at all. Air can only be compressed so far before it becomes a massive obstacle. Air is not infinitely compressible. Not at all.

    In the other case, you will be sending air into more places than you appear to be planning for, because it will leak forward throughout everywhere it can. Dusty, inter-joist, dirty air, getting swirled around by fresh bathroom air, leaking out of switchplates and electrical plugs and door frames and Who Knows Where Else. -- Aghh... Disgusting. Hope this is clear. The dust left over from the initial construction is best left undisturbed. My opinion.

    David

  12. #27

    Default found a ductless vent

    If your code allows it, this will solve your problem.

    http://www.farreys.com/ventilation/e...less_fans.html

  13. #28
    DIY Senior Member lithnights's Avatar
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    Wow prashster, great find!!!

    I will run this by the wife to make sure she likes the "look" of it. Very very picky when it comes to this stuff, but if this eliminates me running ductwork to the outside, then I don't care what it looks like.

    Also, I had someone suggest instead of running it into the joists, to run it down and let it release into the basement (unfinished). That way at least any moisture goes to a large area instead of a confined joist space.

    I thought it was an OK idea. and easy to do..

    what do you think of that option if the wife doesn't likethis fan?

  14. #29
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Doesn't look like that does much to get the moisture out, though.

    -mike

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