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

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by lithnights, Feb 10, 2006.

  1. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    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: Feb 10, 2006
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,013
    Location:
    New England
    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.
  3. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    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!
  4. 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. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    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. Kristi

    Kristi Tradesman Plumber

    Messages:
    176
    Location:
    Vancouver, BC
    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: Mar 15, 2006
  7. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    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. prashster

    prashster New Member

    Messages:
    941
    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: Mar 15, 2006
  9. toolaholic

    toolaholic General Contractor Carpenter

    Messages:
    874
    Location:
    Marin Co. Ca.
    Bad Idea

    DON'T DO IT , hope i was clear :cool:
  10. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    Which is worse then...?

    That was pretty clear. :D

    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. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,641
    Location:
    Cave Creek, Arizona
    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. prashster

    prashster New Member

    Messages:
    941
    I'm serious, try to find a recirculating fan. It'd solve both your problems.
  13. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    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: Mar 16, 2006
  14. Spaceman Spiff

    Spaceman Spiff Architect

    Messages:
    277
    Location:
    Salt Lake City, Utah
    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...
  15. prashster

    prashster New Member

    Messages:
    941
    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.
  16. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    He should still install a fan. No one opens the window in the winter...... that is unless the wallpaper starts to peel. :)
  17. sulconst2

    sulconst2 New Member

    Messages:
    205
    Location:
    old bridge nj
    here's a thought. how about doing a wall mount fan and dropping the exhaust down to the basement then out the back?
  18. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    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..
  19. nelie

    nelie New Member

    Messages:
    1
    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.
  20. sparking5

    sparking5 Electrician, JIW

    Messages:
    97
    Location:
    Midwest
    Brainstormin' here:

    1. Febreeze & radio

    2. Scented Candle & chanting

    3. Perfume & wind chimes (manually moved)

    4. Fresh baked brownies & box fan

    ;)
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