Bathrooms need exhaust fans in order to clear the excess moisture in the air and help prevent the proliferation of mold. The fans should be installed in or near the tub, shower or spa area.
During a bath or a shower, the humidity levels inside the bathroom rise significantly. The absence of a properly working exhaust fan or ventilation traps the excess moisture inside the bathroom and creates a perfect breeding environment for mildew, molds and other microorganisms. If not treated or removed immediately, these microorganisms may cause adverse health problems. Excess moisture can also ruin the paint and the wallboards, promote rusting of fixtures and deteriorate frames and cabinets inside the bathroom. Installing an exhaust fan allows for quality indoor air and prevents costly repairs in the long run.
Interestingly, the installation of bathroom fans is not mandated by most building codes, though it is required that all bathrooms have either a manual or mechanical fan or a window where air can circulate and remove toxic gases and excess moisture. In most states, however, the ventilation code requires bathrooms with bathing fixtures to have intermittent exhaust fans controlled by an automatic timer or a dehumidistat. This is due to the fact that not a lot of people open their windows to promote adequate ventilation.