Please share your thoughts on this Best Practice.

Bathroom exhaust fans are not required by the building code for moisture removal/ventilation as far as I know. The plumbing code requires rooms with toilets to have operable windows or exhaust fans for sanitary reasons. This is called local ventilation. Fans should discharge to the exterior or to an uninhabited vented space such as an attic.

It is true fans can remove moisture from an enclosed space, so discharge piping should be run without traps or sags to avoid condensation. The timers mentioned let the fans run long enough to prevent condensation in the discharge piping.

The International Building Code family does INDEED require either an operable window OR an exhaust fan in bathrooms. I always recommend an exhaust fan in any case...who opens a window in a bathroom in the dead of winter when condensation problems are at their worst?

Rich,

I haven't studied the individual code books since they were combined and don't have a current copy of IRC and I know a lot has changed in 20 years since I studied the plumbing code line by line. It may be a geographic thing also, but when I look at new housing today across several juristictions in my area, rooms with toilets are required to have exhaust fans or operable windows. If the toilet room is by itself (separated from the main bathroom area by a door), the fan is always in the toilet room. A large master-suite type bathroom hardly ever has a fan in the main area near sinks, whirlpool, shower area etc. and a lot of builders are using glass-block windows for light and privacy, but they don't open.

I think exhaust fans are a great idea for condensation control and put them in homes I have built for my family, but it would seem if they are REQUIRED by code for condensation control, they would be required in all rooms with showers or tubs etc, which I don't see.

Maybe I'm just splitting hairs, but when I took my plumbing journeyman's license test (1986), if we didn't note local ventilation in rooms with toilets on the blueprint section they deducted points.

Do you know, has moisture control been added or listed as a reason for fans? Are they now required by code in shower or tub rooms? I've always thought this was a wierd little quirk in the code that doesn't get much discussion.

I have read these posts and I have a question. If the exhaust fan vents to the attic which is ventilated (open on both ends) isn't there still a potential problem with moisture build up on the insulation and consequently the potential for mold? I would love to have an exhaust fan installed but I don't want to have a hole cut into the roof to accomodate the vent.
Can anyone respond?
Thanks

I live in Albuquerque, which is usually very dry. This does not stop mold from developing in bathrooms. At both my last and my current home, black mold develops at the top of the wallboard that comprises the vertical walls of the skylight wells in the bathrooms that have showers/tub combinations. In the winter we can'd stand to run the exhaust fans, due both to the cold and the expense of heating. This raises two questions.
1. Are there quiet, efficient, high-quality bathroom ventilation systems that don't extract the heat from the room?
2. Are there reasonable ways to combine good venting of the bath with humidification of the other areas? Thanks.

Mark,

There are products called HRV's and ERV's that you can add to your home that will recover the heat in your system but these systems can be expensive to install in your house.

A project that you can do your self is to put something called a Tamarack Humitrak in your bath room. This device allows you to activate a fan via Humidity saving you money by not running the fan when you just enter your bath room to brush your teeth.

You can find more information here on the Humitrak

A great resource on why ventilation is important can be found from our local Energy Efficiency Org.
Ventilation


Alec

Thanks very much for the info. The sites look very helpful. I look forward to reading the information.

Mark

Present energy conservation codes do not permit bathroom exhaust fans to be switched with the lights. There must be separate switches. Not running the exhaust fan in the winter during or after humidity-producing activities such as showers is a bad choice, because the cost of whatever heat is saved will be less than the cost of damage produced by the excess moisture.

If your exhaust fan is on the same switch as the lighting, consider having a separate switch installed, so that the fan can be operated only when it is necessary.

As to the problem of exhausting the heat out of the bathroom with the vent fan: only if the exhaust fan is over-sized for the room it serves will this ever be a problem. The fact that mold is in evidence shows that NOT using, or under-using the fan is not a good option. The reality is that most people who object to the exhaust fan do so because it is too noisy. This often causes the homeowner to un-plug or in some other way disable the fan, and mildew accumulation is the result.

Broan, Nutone, Panasonic, and Fantech all make low-sone fan packages which exhaust powerfully, without excessive noise. The exhaust stream should ALWAYS TERMINATE OUTSIDE OF THE HOME, to prevent moisture from condensing into the attic insulation. Also, there should always be a backdraft damper, and a screen at the point of exhaust, to prevent rodents, insects, or birds from nesting in the exhaust duct, and to prevent backwash of unconditioned air into the conditioned space of the bathroom. The exhaust duct should have as short a distance from the bathroom to the exhaust point as possible, with no sags, and should be insulated as it passes through the unconditioned space, to prevent condensation.

Bathroom exhaust fans are great for mentioned reasons. They do change the air and aid in the elevated moisture removal after showers and baths. Sizing exhaust fans is done by using a simple formula: square footage X 8/ 6 = CFM. This is not a code calculation. As a HVAC contractor, we use this formula to calculate the infiltration for a home to determine the equipment size. The fan discharge can be routed through flexible metal hose to a soffet vent. It is not recommended to allow a fan to direct vent into your attic.
The best way to control moisture and condition the air inside your home is with your heating and cooling system. The HVAC system is designed to remove the moisture from your home efficiently. The new high SEER (seasonal energy efficiency rating) equipment has designed moisture rates. Some have dehumidification settings in the thermostat to monitor indoor humidity levely and act to reduce when programmed settings are exceeded.

It is always a good idea to vent your exhaust fans the shortest distance to "The Outside" Either thru insulated duct then thru a Broan 636 damper vent or straight out to the outside into a wall mounted damper vent. The excess moisture from the fans venting into an attic can, and do cause major problems not only on the roof decking such as mold and rotting of supports and depending on what you have as insulation in your attic. The insulation itself.Often it decreases the shingle life as well. With the moisture on the decking and supports freezing and thawing in colder climates the decking and shingles not to mention everything under them and eventually the drywall under them soak this up. Surprise!!!