Okay I actually do understand the purpose of the bathroom fan; it gets the steam out of the bathroom after a super hot shower, right? Well turns out I never turn it on. I suppose I don't shower in sauna temperatures. Also we tend to shower with the door open.

Or, is the point that it rids the room of odors? Thus, the nickname 'fart fan'

The duct from the bathroom fan simply terminates in the attic space. I've been reading the threads explaining the reasons to vent it to the outdoors, but I don't want to. I have a beautiful house with new cedar siding and I don't want to ugly it up with a big vent sitting in the middle of the gable.

So here's the question; why? Can't I simply not use the fan? The steam or stink doesn't bother me. Do I need to put an end on the vent I don't use?

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    It sounds like you're find with the consequences, so it's up to you. The biggest issue will come up if you ever want to sell the house to the normal public that dislikes mold.
    – RQDQ
    Commented Dec 24, 2011 at 23:21
  • One other thing to think about - even if the fan isn't running, hot air rises and most of it is going to end up in your attic. Steam will just have a little more time to shed its moisture in your bathroom when the fan's not running. Commented Dec 27, 2011 at 14:07
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    Do you "want" to be sick? Because mold growth from excess humidity will definitely help there. Commented Jan 3, 2012 at 21:10
  • Is not advisable,your hearth and environment must be watched,create a window on your bathroom wall to be free from fan brake down and odors in your bathroom.
    – user25229
    Commented Sep 15, 2014 at 12:00
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    You will all be happy to hear that I've recently run the hose to an exterior vent.
    – Trout
    Commented Aug 30, 2015 at 20:13

6 Answers 6


Since yours vents into your attic space I would never use it either. Probably the biggest use of a bathroom vent fan is to help keep mold down in bathrooms, especially in humid areas. Lots of lawsuits against housing tracks have happened in humid areas where builders just put the cheapest fan in and a couple years later the residents find mold. Most bathrooms that are bigger than a closet have undersized fans and don't really do anything but make noise.

Building code changes will happen, if not all ready changed, that homes will have to have a certain air exchange per hour. This is because the modern homes are being built pretty much air tight, or about as close to it as you can get with doors, windows and other entry points for air to get in a house. Builders are starting to use bath fans for this, and a lot of them are being designed to be used 24/7, with very little noise.

Either way, do not pump moisture into attic spaces.


If your bathroom doesn't have a window and no fan then that all that moist air is going to create a perfect environment for mold and other unpleasant things.

Also, excessive humidity will probably make it's way into your walls and I you have a wooden house then it will start to rot.

That's why it's a bad idea for a vent to exhaust to the attic. It's just going to cause same problems there instead of bathroom


As others have said you don't want to let humid air into your attic space. You will not only get mold as others have mentioned, but the moisture will reduce the effectiveness of the insulation in your attic.

While I understand not wanting to have a vent on your roof, I would recommend either getting a low unobtrusive roof vent on the back slope of the roof or possible putting a vent out the eave or wall.

here is an example showing a dryer vent

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    If you vent out the eave and have soffit vents pulling air into the attic (for ventilation), you'll end up sucking the moist air up into the attic anyway. You can only vent to the eave, if you do not have soffit vents for roof ventilation.
    – Tester101
    Commented Jan 3, 2012 at 21:06
  • Jim, this is brilliant. If I vent out the soffit it will be the most 'invisible'. I realize the drawing is a dryer, but the vent path is viable, right? Do they make 'eve vent hood' in many materials? sizes?
    – Trout
    Commented Jan 9, 2012 at 19:27

Moisture removal.

"Every bathroom requires an openable window that provides at least 1.5 square ft of air flow area when open – 2006 IRC [303.3] OR mechanical type ventilation: 50 CFM intermittent or 20 CFM continuous operation – 2006 IRC [303.3X]"

See this related thread for other comments: How do I refinish a bathroom ceiling after it got moldy and peeled?

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    thanks for quoting the code. but you didn't really answer the question. I want to know what you THINK. How is it different to have a window that I never open rather than a fan I never operate?
    – Trout
    Commented Jan 11, 2012 at 2:10
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    @Trout I think the point is to start opening the window to remove the moisture and prevent mold, this question is a couple of years old so I hope you've started :-)
    – MDMoore313
    Commented Dec 28, 2013 at 20:22

Why do you use a bathroom vent fan? To remove moisture.

Why remove moisture? Moisture penetrates latex paint and sheetrock. Ceiling sheetrock will retain so much moisture, you can see the paper backing is damp.

As I found out much to my chagrin way back when I had to open up the wall on a bathroom that had a long failed power vent (black mold). Needless to say, the walls came out, a new fan went in and was used ever after.

Other tales from the Pacific Northwest brought to you by incessant damp in bathrooms, "The Amazing Descending Throne", an oft told tale by one of my Dad's friends who had it happen while he was sitting on it. Plywood subfloor doesn't hold up too well to the damp either.

  • Though a contractor somewhere needs a bit of karmic revenge as it's a crime against physics and materials to vent moist air into an attic space. Commented Aug 30, 2015 at 22:37

The purpose of a bathroom exhaust fan or bathroom window is to vent humid air outdoors.

When I bought my house, it did not have a bathroom fan. I had grown up in a house with a bathroom fan, and thought perhaps it wasn't necessary to vent the moisture, after all, since it didn't make sense to me to open the window in the winter.

I was wrong. After a year or two, the ceiling texture started cracking and falling off, and around the same time I noticed black spots developing on the ceiling, as well. Apparently the purpose of venting moist air is to prevent mold from growing and to prevent the moisture from damaging your ceiling, walls, and cabinets.

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