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

  1. #1
    DIY Senior Member lithnights's Avatar
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    Default Can I vent my bathroom exhaust fan into a joist bay?? No moisture...

    I am remodeling the 1st floor of my 2 story home.. moving a bathroom 15 ft over. Supply, vent, and waste are not a problem. The exhaust fan may be.

    I want to install an exhaust fan to 1) eliminate odors and 2) provide a slight noise to muffle any bathroom sounds. But the bathroom does not border an outside wall and thus I can't run my exhaust fan to the roof or exterior wall or outside soffit.

    Since there is no shower and thus no major moisture can't I just vent the exhaust fan into the joist bay above the bath? I'm guessing the textbook answer is no, but what is the major downside and ill effects of doing this?

    Thanks in advance!
    Last edited by lithnights; 02-10-2006 at 04:59 PM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on which way the joists go, whether there is any blocking, and some who knows what, you might be able to run the duct through the ceiling to the outside wall. I have a bathroom in the middle of the house and that is how they did it - a duct through the ceiling to the outside wall.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member lithnights's Avatar
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    Quote Originally Posted by jadnashua
    Depending on which way the joists go, whether there is any blocking, and some who knows what, you might be able to run the duct through the ceiling to the outside wall. I have a bathroom in the middle of the house and that is how they did it - a duct through the ceiling to the outside wall.
    Good point. The joists run front to back of the house, but it would have to run 8 feet to the front and then come out the soffit there. Not exactly what I wanted. Also, there is a plumbing waste line cutting through the joists perpendicular so I'd have to get the flex tube around that (which probably means crushing it down a bit in that area.

    I guess my real question is... IS ALL THAT NEEDED IF THERE IS NO MOISTURE? CAN'T I JUST ATTACH A 2 FT PIECE OF DUCT TO THE FAN AND JUST LEAVE THAT HANGING BETWEEN THE JOISTS?

    Thanks!

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    Master Plumber master plumber mark's Avatar
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    Talking duct fan

    its probably best to get it somewhere where it can
    ventilate in cas their is moisture


    use the dlexible poly pipe and take it over to the
    soffit vent if you can... I have seen electircians
    hang those bath vents and attach -- nail them up to the
    roof vents too....

    seems to work ok

  5. #5
    DIY Senior Member lithnights's Avatar
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    I agree that it is probably best to get it somewhere but in my situation that would be very difficult.

    Seeing that this is a downstairs bath with no shower or bath and minimal water use, where would moisture come from anyway?

    I checked my father's house (built in 1970) and he has a downstairs vent exhausting right into his joists. Like me, no shower/bath and thus minimal moisture. He has never had any mold/moisture issues.

    So would it really b e so bad to vent it into a 4 foot flex duct that just rests on the joists? I'm sure it's not code, but is it really that crucial for a bath with minimal moisture to begin with?

    Thanks,

  6. #6
    Tradesman Plumber Kristi's Avatar
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    it sounds like you know what you want your answer to be... no one is going to tell you "yes, go ahead and vent it straight into the open attic" because they all know that it's not a job they would want to stamp their name to (pro OR homeowner). It's not the right way to do it. If you are a handy dandy homeowner who has rationalized the lack of moisture portion of your exhaust dilemma, then you should continue forging ahead with your plan and see what happens. It will not have a disastrious outcome, it will turn into another one of the millions of homes out there when a professional sticks his head up there and says "who the effing eff did this effing job!? They should effing lose their license!"... imho
    Last edited by Kristi; 03-15-2006 at 11:07 AM. Reason: additional comment

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    DIY Senior Member lithnights's Avatar
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    You're right, I was hoping someone would reply and say, "yea, that's not such a crazy idea, go ahead!"

    I'm still waiting for that answer!

  8. #8

    Default I wonder...

    ...if they make recirculating bathroom exhaust fans.

    Ventless stove range hoods are easily found. They circulate odors and grease through charcoal filters and recirculate the air back into the kitchen. I imagine a version has to be available for a bathroom.

    They don't extract moisture, but this isn't your issue.

    Shoot, if you can't find one, why don't you just put a ventless range hood in your ceiling. That'd be kinda funky!

    I believe codes are there to protect laypeople (like me). The ramifications of what we do are not always intuitively obvious to us. Staying within code provides reasonable assurance that what you've done is safe. Further, not following code could void an insurance claim.

    Don't take some internet forum as the final word on this. You better call yr construction offc. That much'll be free.
    Last edited by prashster; 03-15-2006 at 01:29 PM.

  9. #9
    General Contractor Carpenter toolaholic's Avatar
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    Default Bad Idea

    DON'T DO IT , hope i was clear

  10. #10
    DIY Senior Member lithnights's Avatar
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    Default Which is worse then...?

    Quote Originally Posted by toolaholic
    DON'T DO IT , hope i was clear
    That was pretty clear.

    OK then, so what is worse then...
    1) to have a vent/fan exhaust directly into joists (not the attic.. this is 1st floor bath) OR
    2) to not have the vent/fan there at all?

    Keep in mind, the main reason I want this thing is for smell exhaust and to add a slight noise to the bathroom (for privacy reasons).

    Thanks!!

  11. #11
    Moderator & Master Plumber hj's Avatar
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    Default fan

    If the fan is exhausting into a closed area it is not going to move any air, so that takes care of the smell part, and a "white noise" generator would create the sound you want. Japanese women flush the toilet to mask any "sounds".

  12. #12

    Default

    I'm serious, try to find a recirculating fan. It'd solve both your problems.

  13. #13
    Plumber Cass's Avatar
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    The effort you expend to do it right will more than compensate for the lack of problems it will create in the future.

    Moisture from the bath/shower will ruin the bathroom/ area vented to, if not vented right. If vented into the joyce area between floors, and not out, you will have mold growth and damage to wood/flooring. Bath fans can be vented out the side of the house and don't have to go to the attic.
    Last edited by Cass; 03-16-2006 at 05:48 AM.

  14. #14
    Architect Spaceman Spiff's Avatar
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    prashster, check out IRC 1506.2, a recirculating vent may not be allowed by code...
    I've been trying to find the code refrence, but around here if you have a openable window, you don't need a vent fan. IMC chapter 400 comes to mind...
    Spaceman Spiff aka Mike

  15. #15

    Default

    I know around here that even if you have a 1/2 bath, then you have to have an externally vented bath exhaust fan if no window. I thought, though, if for whatever reason the original poster's town didn't have the same req'mt, and they were just putting one in for aesthetics, then a recirculator would have been ok.

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