In my professional opinion, the most ridiculous allowance in the Building Code was letting bathroom exhaust be handled by having an operating window in the bathroom. Really? This is Canada, and it is too cold to open any windows seven months of the year —too bug infested to open windows for three months of the year, and too hot the other two months.
Not properly exhausting warm, moist air results in damage to the wall and ceiling finishes and worse, mold growth and health issues.
We often inspect home electrical systems and find the exhaust fans not working. Closer examination shows them disconnected from the power supply. The common excuse for this tampering is “the fan’s too noisy”.
There is good news. For fans installed between floors and there is no access above, all the major fan manufacturers now produce a “quiet” model. This unit can be installed with no damage as a replacement/new install in any bathroom. For fans installed where there is access to the attic, a silent fan can be installed remotely(means you can’t hear the motor running but you can hear the air moving).
Properly ducting bathroom fans
Insulated duct should always be used in a fan installation, even between floors, to prevent condensation. If the fan is vented out the side wall of the house, the exterior vent should have a “draft-stopper” feature to prevent wind from blowing back into the bathroom. Soffit mounted vents don’t require this feature, but should have an animal screen to keep critters from moving in. Roof mounted vents come with a weighted metal draft/animal stop. It is important that the roof mounted vent be placed high enough on the roof that ice dams do not form at the soffits.
To ensure that the fan is used most efficiently, you can install a timing control or occupancy sensor for an exhaust fan so it will stay on to clear the room after the occupant has left. This can be very valuable so the humidity after a long, steamy shower is removed from the bathroom. An alternative to ensure that the fan is used with each bathroom use is to have the fan come on with the lights.