Since time immemorial, bathroom exhaust fan code requirements have remained relatively constant. One of two choices is required for light and ventilation in your bathroom:
- Light and ventilation by means of a window, which has a minimum size of three square feet, half of which is operable.
- An artificial light source (operable by a switch) and mechanical ventilation with a minimum size of at least 50CFM, in lieu of a window, and in compliance with section M1507 of code, which allows for outdoor ventilation only (no recirculation, no venting to the attic/crawlspace).
Looking for your tape measure? You might want to put it down – unless you’re a fan of “venting” through that window you’re hoping is 3 square feet when it’s snowing outside or during the next summer heat wave.
Wait a minute - does my bathroom need a fan?
Despite this archaic loophole and the time-honored tradition of relying on a bathroom window (which – let’s face it – typically stays closed 90% of the time) for ventilation, and though you may technically be up to code with those three square feet of glass and screen, it’s just not enough.
A bathroom exhaust fan serves many important purposes
What is the exhaust fan in the bathroom for?
- Smells.It’s the bathroom, it should go without saying it’s in the best interest of retaining family peace to have a reliable way to control smells.
- Humidity control.From putting on your makeup sans-sweat to effectively using your hair dryer, humidity control in the bathroom is essential to comfort. It’s also essential for…
- Mold prevention.Excess moisture buildup on surfaces increases the likelihood of smelly and potentially dangerous mold and mildew proliferation. Keeping air dry with a bathroom exhaust fan can prevent this.
- Paint and building materials preservation.If your paint is peeling, this is a sure sign of excess bathroom humidity. Left unchecked this moisture can cause damage and create cleaning headaches on tile, tubs, flooring, and wall surfaces, potentially resulting in the early replacement of these materials – and the insulation and structure underneath – if left unchecked to result in mold and later, rot.
Proper ventilation is key
Where does bathroom fan vent to? As stated above, it must ventilate outside your home. Duct runs must be short, aimed in the proper direction for airflow, installed in a way that limits condensation (which could drip through and rot your ceiling), and include properly operating backdraft dampers before ventilating through a nearby exterior wall or the roof. This must also be properly cut and sealed to prevent leaks and rot. Fan size must also be properly selected to compensate for ductwork losses, as static pressure in the system can reduce airflow below the necessary 50CFM. Electrical must also be safely run to a switch and/or timer, following manufacturer instructions for GFCI requirements exactly. For these reasons and the sheer complexity of selecting an exhaust fan that is the right size for your bathroom’s setup and needs, professional assistance with fan selection and installation are highly recommended.
Bathroom exhaust fan requirements might feel overwhelming, but they don't need to be with the help of Mr. Electric.
