Bathroom exhaust fans come in a number of different types but the most common are rectangular with a plastic cover which is either white or off-white, although other colors are available as well. Other than for aesthetics, bathroom exhaust fans also have different noise ratings and the air flow is variable.
For most homeowner’s one primary consideration when purchasing an exhaust fan is the amount of noise it generates, a quiet fan is by far the most desirable. Fans come from the manufacturer with a “quietness rating” which is expressed as a sone. The higher the sone rating, the noisier is the fan. In most instances the lower sone rated fans which are quieter are also more expensive. A very good compromise is an exhaust fan with a sone rating that falls in the range of 0.5 to 1.2; this will be an acceptably quiet fan at a reasonable price.
For the normal bathroom exhaust fan to do its job properly it must produce an airflow of about one cubic foot per minute (CFM) per square foot of bathroom floor space. If the bathroom under consideration measures five feet by eight feet, the floor area is 40 square feet and the CFM rating of the fan should be at minimum, 40 CFM. Larger bathrooms which have a shower as well as a whirlpool tub usually require the installation of twin fans, one located at each end of the room, in this way the moisture will be extracted efficiently.
Although most bathroom exhaust fans are just fans there are models which incorporate heat lamps, lights and night lights. If the exhaust fan provides the primary source of light in the room then it is important that it can handle a bulb which will provide adequate light, depending on the size of the room this could be 100 watts or more. Anything less than that, say 40 watts will be too dim to provide adequate lighting. Night lights have a very small light output, no more than four watts. Heat lamps can be incorporated into the fan; they are usually rated between 100 and 250 watts.
Both square and round bathroom exhaust fans have an integral grill which is designed to appear as if the fan was a flush mounted ceiling fixture.