A bathroom exhaust fan is a one-way portal connecting your bathroom to the outdoors. The fan pulls air through the bathroom and carries fumes and moisture to the outside through a wide hose or pipe. The ability to draw moisture from the bathroom alone makes an exhaust fan in a full bathroom a valuable tool against mildew and mold.
If lighting is limited in the bathroom, or if the fan will replace an existing ceiling light, then go with an exhaust fan assembly that includes a light. The wall switch to operate the mechanism can be set to a single switch that turns both the light and the fan on at the same time, or two switches can be used to operate the fan and light separately.
An exhaust fan with a heat lamp (bulb) or a heating element can augment your current bathroom heating system or replace it, depending on what type of equipment you buy. Controls for the fan and heating portion of the unit will be separate so the fan or heating portion can be used independently or simultaneously.
A timer allows you to choose how long to run the fan. This feature is particularly helpful in a windowless bathroom or non-air-conditioned space when a boost of fresh air is needed or if a steamy shower left moisture on the walls. You can turn the timer to 20 minutes just before leaving the bathroom to let the fan finish clearing the room.
Not all exhaust fans are built to the same quality level. Some models are designed to reduce vibration and noise. If you plan to run the fan after the room has been vacated and with the door open, you may want to pay extra for a fan with a low sones rating so the noise of the fan is not heard in other areas of the house. Sones are a measurement of appliance noise. 1.5 sones is very quiet.
Most bathroom exhaust fans are mounted in the ceiling, however, some situations like a ceiling that does not have room for the fan or the exhaust hose, may dictate a wall mounting.
According to the Home Ventilating Institute (see Sources below for link), a bathroom of less than 100 square feet should have a fan capacity of 50 CFM (cubic feet per minute), indicating how much air the fan can move. The rating will appear on the box. For a room greater than 100 square feet, there should be at least 50 CFM’s each for a toilet, shower or bathtub; and 100 CFM for a jetted tub.