My son is having a master suite added to his 1970’s home. The bath is quite large, consisting of two separate rooms, one containing a shower and a toilet, the other room containing a large whirlpool tub and double sinks. The GC was not planning to put an exhaust fan in the room with the tub, saying that the fans were only required for methane gas in the toilet room. I always thought exhaust fans were supposed to be for humidity, not methane gas. Of course I am going to install a fan anyway, but as far as the requirement, who is right? Besides, how can methane gas enter a properly plumbed bathroom anyway? And if it did enter the room, the spark from the motor would set it off! This guy is full of “methane gas”, no?
Mechanical ventilation isn’t even a requirement if the bathroom has an openable window. Practically speaking, they should be provided in new homes because who opens the window when taking a shower in February?
I have seen “fart fans” in enclosed water closets and no mechanical ventilation (or window) in the area where the shower is located and I have recommended them there. Moisture is the structural concern, not methane.
Code is below…
R303.3 Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which must be openable.
Exception: The glazed areas shall not be requiredwhere artificial light and a mechanical ventilation system are provided. Theminimumventilation rates shall be 50 cubic feet perminute (24 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside.
Brian,
Basically the "Fart Fans" which we all call them as well are really their for venting the moisture out as if it is NOT vented out will cause issues with the paint and possible wall board and again possibly fungus growth.
They are required in a bathroom as stated above with no window...or a window that is not openable......But where are they required....basically if the bathroom has a seperate small area for a toilet it would not be considered a bathroom area on it's own....MUST have toilet and sink or sink and shower and well you get the picture...
We install these ( not sure why the electrician gets stuck with these now days..but we do....sigh....Never wanted to be a DUCT man..)..anyway....sicne the tub area is in common area with sink it is ruled a bathroom...and with no window....a vent is required.
Many are putting one in the small seperate toilet area...BUT 100% of the builders I work with...will not......one in the MAIN bathroom and they are DONE......and the AHJ's do not have a problem with it based on the defined term of bathroom.
Hope this helps
Depending on the room size, I would highly recommend an exhaust fan be installed to vent from 50 to 100cfm’s.
Any Contractor that tells you a bath area requires no exhaust fan is quoting some minimum code of some sort and is full of methane gas himself. Better not bring him in this room. ha. ha.
Whether required or not, some sort of preventive action is required to prevent exccessive humidity and moisture acummulation of the room environment.
This will elliminate or prevent any future problems with paint, wallpaper, or drywall components.
Marcel 
hey thanks for the info people…I knew I was right!:mrgreen:
He is full of something…but it ain’t methane gas.
Funny how people will not use the bathroom exhaust fan (too noisy, expecially after the first year and no one cleans them), but will complain to high heaven about mildwew on the tile and mold growing behind that Gawd Awful plastic wall paper that some people just love to put in bathrooms.
Juts like the people who will pay 10s of thousands of dollars for a flood control system, but not $40 for downspout extensions.
Some people just don’t know how to take care of a house.
And some GCs don’t know how to build them.
Which code was quoted above? About half of the new construction I run into they either lay the bathroom vent pipes on the inside of the perferated metal soffit or run the pipe up to ‘near’ a roof or ridge vent.
I have seen so many ‘new’ houses with rotted roof decking in the past year you would not believe.
Hope this helps;
2003 IRC M1506 Mechanical Ventilation.
The vents all have to be routed outside in the Florida code. Nothing can terminate anywhere in the attic.
Greg;
But I bet a few people still do it that way, don’t they?
Including mine, how do you like that? Is’t that pathetic? Don’t worry, I am renovating my bathroom for the third time in 16 years, I promise you when I install my new fan and light that it will make it to the roof. Promise. Sorry I waiting this long. At least it was exhausting through the soffit vents so it did not cause any problems, I checked.
Sounds like a Carpenter with doors that rub and plumbers with leaky faucets dosen’t it.??
Marcel 
Two things I like on Bathroom fans are
One very quiet ( Cost more but people use them more) .
Two on a timer so they do get used longer but not left on constantly.
Roy Cooke sr
Hey; Roy, hope you are well and always a pleasure to share notes.
I agree with your statement 100% and I am sure my wife will keep reminding me of those facts. ha. ha.
As they say, third time your out, right? This time, best four piece tub shower unit, best vanity top available other than granit, new ceiling , new tile floor and walls, and paint. This reminds me, I dispise working in bathrooms. ha. ha.
Oh well.
Marcel