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Thread: Bathroom vent fans, good or bad?

  1. #16
    Join Date
    Dec 2010
    Location
    Evanston, IL
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    1,265
    As nearly everyone has said, yes to a fan vented to the outside. A big yes to a timer switch. Not only does it shut the fan off if you forget, it also runs the fan for a sufficient amount of time to remove the humidity even if you leave the bathroom quickly and turn off the light.

  2. #17
    Join Date
    May 2009
    Location
    houston tx
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    624
    Here in SE TX venting into the attic doesn't add to the humidity. I really doubt it does anywhere.

  3. #18
    Quote Originally Posted by mark kosse View Post
    Here in SE TX venting into the attic doesn't add to the humidity. I really doubt it does anywhere.
    I get mildew from air with a dew point of 80F condensing on walls at 70F in the bathroom when the teenager forgets to turn on the fan after showering. Now imagine venting air with a dew point of 80F onto a bunch of rafters with a surface temp of -10F

    Rot and mold from condensation are sadly common around here, and the reason why there are those kinds of codes around venting, vapor barriers, make up air, etc. I imagine it would be different in the south of the country where indoor air is frequently dryer than outdoor air. We actually get both, dryer indoor air in the summer and much wetter air in the winter, but the difference in humidity and dew point is much more extreme in winter than summer.

  4. #19
    Join Date
    May 2007
    Location
    Newburgh, Indiana
    Posts
    884
    I've seen mold in attics near the vent fan exit. Also had a mold problem in a house we bought to remodel. The previous owner shut off the power and basement filled with about foot of water before I could get possession and address the problem.
    Life's too short to use old sandpaper.

  5. #20
    1250 cm, is that a 5hp exhaust fan?

  6. #21
    Join Date
    Jun 2008
    Location
    So Cal
    Posts
    2,368
    All bathrooms should have a fart fan.
    Thatís what we call them in roofing business they usually end with a t-top on the roof.
    Aj

  7. #22
    Join Date
    Feb 2003
    Location
    Griswold Connecticut
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    6,384
    Quote Originally Posted by mark kosse View Post
    Here in SE TX venting into the attic doesn't add to the humidity. I really doubt it does anywhere.
    Mark
    Not so much humidity, but condensation.
    Warm, moist, bathroom air, venting into an attic, that is below freezing, is going to be a problem after time. Might take twenty, or thirty years, but it will one day have to be remediated.
    Thousands of examples in New England houses.
    Last edited by Mike Cutler; 08-23-2019 at 5:23 PM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  8. #23
    Join Date
    Oct 2006
    Location
    Minneapolis, MN
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    3,884
    Quote Originally Posted by Mike Cutler View Post
    Put the vent fan in. Put it on it's own circuit with a timer.
    Why on a separate circuit? They don't draw anywhere close to 15 amps. You can connect to lighting circuit at the switch box without having the fan go off and on with the light. NEC requires a separate 20 amp circuit just for the receptacle that can't be used for the fan.

    I have my bath fans on digital times that can do 10, 20, 30, or 60 minutes. I normally use 30 minutes for a shower.
    Last edited by Brian Elfert; 08-25-2019 at 1:40 PM.

  9. #24
    Quote Originally Posted by Jon Nuckles View Post
    As nearly everyone has said, yes to a fan vented to the outside. A big yes to a timer switch. Not only does it shut the fan off if you forget, it also runs the fan for a sufficient amount of time to remove the humidity even if you leave the bathroom quickly and turn off the light.

    What Jon said. X2

  10. #25
    Join Date
    Aug 2007
    Location
    Dickinson, Texas
    Posts
    6,542
    Blog Entries
    1
    We have two bathrooms and two fans. They work.

  11. Simple answer. My parent's bath room vent fan was operated by a rotary switch that turned the fan off after a few minutes. I think it could be turned all the way to 10 minutes and then shut off. House built in 1960 and still has the same switch on the wall. This one goes off after 30 minutes. https://www.1000bulbs.com/product/33...SABEgLzb_D_BwE

  12. #27
    Join Date
    Sep 2010
    Location
    Livonia, Michigan
    Posts
    675
    My house has a full bathroom in the basement with a vent fan and no window. The upstairs bathroom has no fan but does have a window. Guess which bathroom has the mold problem? If you guessed 'upstairs bathroom' you would be right.

    What really helps is the room has a pocket door separating the bathtub and the sit-upon from the rest of the room. The fan is about as small as they come but can clear the 5' X 6' space with no problem. It has a 30 minute timer on it, if it goes bad I might get a one hour timer. If the pocket door isn't closed 30 minutes doesn't cut it.

    My brother built a house and decided to install a single fan for all the bathrooms and ran ducting to each bathroom. Each room had a timer that ran the shared fan. A few months after living there one of the rooms stopped getting any ventilation. He found the flexible ducting full of water. So he had his SIL hold a 5 gallon bucket under the bathroom vent while he lifted the ducting up to drain it.

    It was the furthest room from the fan. There was a lot of duct. And a lot of water. The bucket wasn't nearly big enough.

    After looking at all the options (insulation, smooth PVC) he ended up installing a dedicated fan for that room. The length of duct to the shared fan was too long. A direct path to an outside wall was was shorter. The remaining rooms didn't have a problem.

    A friend was redoing the bathroom in his quad level house, pulled out the bathroom fan and found no duct hooked to it. None. The fan just blew into the space above the bathroom ceiling and below the floor of the bedroom above it. He showed that one to me and asked, "Where is the air going*?" His solution was to stop using the shower in that bathroom and use another one. Nice that he had the option.

    -Tom

    *He said other things but I'm trying to be nice to the mods.

  13. #28
    Join Date
    Oct 2006
    Location
    Minneapolis, MN
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    3,884
    Quote Originally Posted by Tom Stenzel View Post
    My house has a full bathroom in the basement with a vent fan and no window. The upstairs bathroom has no fan but does have a window. Guess which bathroom has the mold problem? If you guessed 'upstairs bathroom' you would be right.
    Most people don't want to open a window when it is hot or cold to ventilate the bathroom. Code was (maybe still is) to have either a window or a fan in a bathroom.

  14. #29
    Join Date
    May 2009
    Location
    Northwestern Connecticut
    Posts
    126
    We have a 1972 vintage house, plenty of air exchange (i.e, not an energy-efficient, air tight house). The bathroom fan, installed about 10-15 years ago, has a built-in humidity sensor, and you can set the fan switch to auto or manual, or off. So you can reduce humidity from a shower, or you can exhaust noxious smells. It vents outside, not into unheated attic space.

  15. #30
    Join Date
    Jan 2018
    Location
    Vancouver Canada
    Posts
    184
    Like everyone else yes to the fan, and ALWAYS to the outside.
    I did have a cheapie Braun 50CFM, and tossed it when I went to a cage type Panasonic - quieter and double the CFM.
    Young enough to remember doing it;
    Old enough to wish I could do it again.

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