Many people think of a shower exhaust fan —if they think of it at all— as being a mere accessory to their bathrooms. A handy convenience which clears moisture from the air and mirror. It allows them to get through their daily routines more quickly. In reality, however, having the correct shower exhaust fan matters more today than ever. New homes are built to be highly insulated and practically air tight in order to save energy. That makes proper bathroom ventilation absolutely essential to preventing damage.
Without this ventilation, humidity levels remain high within the bathroom. And that creates the perfect breeding ground for mold, mildew, and a wide range of harmful bacteria. Likewise, paint eventually cracks and peels, wallboard becomes damaged, fixtures rust, and the bathroom door may even warp.
In addition to installing and using your bathroom fan properly, ensuring that it is properly duct to the exterior of the house and that you run it for a full thirty minutes after you shower or bathe, it’s essential to choose the right type of fan. A fan that is not powerful enough will not provide adequate ventilation. And will therefore leave damaging moisture hanging in the air for longer than is permissible.
Before considering matters of style, you should look at a fan’s air movement capacity. It is typically measured in cubic feet per minute (CFM). For the vast majority of bathrooms (excluding those which have special features, such as ceilings higher than 8 feet) this works out to one CFM per square foot of bathroom area. As such, if your bathroom measures, for instance, 7 feet by 10 feet, you will need a 70 CFM fan.
Very large bathrooms (those which measure more than 100 square feet), may need additional ventilation; usually an extra 50 CFM for each toilet, shower, and/or bathtub present (100 CFM per jetted tub).
However, one should not feel confined to these requirements; they are merely the suggested minimums and it’s often worthwhile to overshoot them somewhat. Doing so ensures adequate ventilation and often requires little extra energy consumption.
Once you have chosen the right CFM level to meet your needs, you should narrow down your choices based on the amount of noise you find tolerable. We measure bathroom fan noise levels in what is called “sones”. 4.0 sones is equivalent to the volume most people watch TV at, for example. Whereas 1.0 sones is only about the same as the low hum a refrigerator emits. If you often spend time in the bathroom while the shower exhaust fan is on or have concerns about disturbing others in your house, aim for a sone rating of 1.0 or less.
Finally, consider matters of style and additional “luxury” functions; in addition to selecting a fan with the look and feel that suits your bathroom décor, you may wish to choose a model with a light, a heating element, or a timer or humidistat to facilitate automatic operation—today, there exists a truly remarkable variety of fans to choose from.