Purpose of Bathroom Exhaust Fans
Bathrooms, especially those with showers, generate a significant amount of moisture. If this moisture is not vented out of the house, it condenses on mirrors, bathroom fixtures, and walls which creates an environment where mildew and mold can grow. Current building code requires that an exhaust fan be installed in every bathroom to remove excess moisture.
Routing Bathroom Exhaust Fans Out of the House
While most houses since the 70’s have exhaust fans installed in bathrooms with showers, many of these fans do not actually vent their moisture out of the house, but simply send it into the attic space. This issue can cause moisture to condense on the underside of the roof in the attic which leads to rotting of wood members or mold. While completing any insulation or air sealing work in the attic, all bathroom exhaust fans should be ducted out of the attic to eliminate the potential for this problem.
Installing New Bathroom Exhaust Fans
Some homes have bathrooms with showers that do not have exhaust fans. As the house is made tighter through air sealing work, moisture will take longer to naturally dry out from these bathrooms and a moisture problem may be created. Because of this, we recommend installing a bathroom exhaust fan in any bathroom that does not currently have one if any air sealing work is being completed in the attic. We typically recommend the installation of ENERGY STAR® Rated Panasonic Whisper fans because they are very quiet and energy efficient. These fans have the option to be run with condensation sensors or continuous ventilation modules to ensure effective moisture mitigation regardless of who is using the bathroom.
An Atlas Energy Auditor can determine if your bathroom exhaust fans need to be routed or if you should install a new one.