How Bathroom Exhaust Fans Work

The functional importance of bathroom exhaust fans cannot be overstated. Bathrooms are damp places. Daily showers and running water drive up the humidity in these rooms, creating potentially unhealthy environments and creating a breeding ground for toxic molds and bacterium.

To ensure that the indoor air quality of the bathroom space is maintained, we look to bathroom ventilation systems to move the foul air from the room and exhaust it to the outdoors.

Fortunately, the bathroom exhaust fans that we rely upon to accomplish this goal have come a long way from the loud, eye-sore boxes of yesteryear. Today’s bathroom exhaust fans are quieter, decorative pieces that can double as overhead lighting and perform their task with minimal interruption to the peaceful calm we’ve come to expect from our bathroom havens.

Overview of Bathroom Exhaust Fans

The bathroom exhaust fan plays a critical role in maintaining the indoor air quality of not only the bathroom but the whole home. Its primary role is to extract humid air from the room and expel it outside the home.

While showering or bathing, shaving or brushing your teeth, any bathroom activity utilizing water results in the build up of vapor particles in the air, becoming the culprits of a number of problems. Fogging mirrors should be the least of your concern. The vapor buildup over time can cause acute damage to tile, grout, and flooring.

It can also lead to the breakdown of cabinet finishes, cracked and peeling paint, and rusting of hardware and fixtures. In a worst-case scenario, an ill-fitted or non-existent bathroom ventilation system can permit the growth of mildew and mold, which can be potentially toxic to the homeowner.

Purpose and Function of Bathroom Exhaust Fans

So how do bathroom exhaust fans actually work? In simplest terms, bathroom exhaust fans have a motor that runs on electricity. That motor powers a fan, which draws moist air up through the fan and into ductwork (generally speaking) that – if installed correctly – exhausts to the outside, often through a soffit vent or eave vent hood.

Bathroom fans will vary by power, often rated in CFM (cubic feet per minute), which is a measurement of how much air the fan can draw from the room over a period of time. The higher the CFM, the more air the fan can move. Generally speaking, the bigger the bathroom, the higher the CFM you’ll want.

Bathroom Exhaust Fan Options

Ceiling-mounted

Ceiling-mounted bathroom exhaust fans are perhaps the most common, and popular versions of the fan options. As the name indicates, these fans are installed directly in the ceiling of the bathroom. The ceiling-mounted exhaust fan removes moisture and odors from the bathroom by expelling the suctioned air from the room, via the housing, through ductwork, and out the roof or overhanging soffit.

The fan works by pulling the air up through the downward vent. As the air is forced upward, the internal blower motor pushes it through the ductwork in the direction of its final destination, be it the roof, or soffit. These particular exhaust fans are available with multiple attached features, such as light, heat, or decorative finishes.

Inline

Another choice in bathroom ventilation is opting for the inline bathroom exhaust fan. These fans work in the same fashion as the ceiling-mounted fans, but have a completely different design. This type of fan is not rested on the ceiling of your bathroom, but instead, it is installed to a joist in the attic space directly above, or slightly away from the area. All that is exposed in the bathroom ceiling is a flush, louvered vent.

The advantages of the inline bathroom exhaust fan include sound reduction (because it is mounted in the attic), the usage of only one unit, but allowing for multiple exhaust points, and the elimination of power limitations.

These fans work by sucking the moist air into the attic-located housing unit. The air travels through ductwork that is connected directly to the ceiling vent. Another duct runs from the housing to the exterior of the home, again being, the roof, or overhanging soffit. The blower motor then propels the air from the housing unit through the ductwork connected to the exterior of the home.

Wall-Mounted

Wall-mounted bathroom exhaust fans are also exactly as the name indicates. They are installed directly on an interior, or exterior wall of the bathroom. These type fans are often used in bathrooms with cathedral ceilings, no above attic space, or where overhead lighting or skylights consume the ceiling area. The advantage to a wall-mounted fixture is the lack of need for any ductwork, if mounted on an exterior wall.

However, they can be installed on interior walls, in which case the ductwork would run through the wall, to the outside. The operation of this particular exhaust fan is comparable to the ceiling-mounted and inline versions. The stationary humidity is suctioned to the unit, where the housing cubicle gathers it, allowing the blower fan to drive the air directly out of the wall, to the exterior of the home.

Combination Units

A number of bathroom exhaust fans on the market today boast additional features. Lighting, heating elements and even humidity sensing capabilities are much more common these days. Just about every combination therein can be found in ceiling-mounted, inline and wall-mounted models. Expect to pay a bit more for these multi-taskers.

Installation

Your wiring options are dependent on the model of fan chosen. One option includes direct-connect to the existing light switch. In this case, whenever the light switch is turned to the on position, the fan will also be automatically turned on. Another option is to wire the fan to operate independently of the bathroom lighting.

If possible, the latter is the better option, as it is advisable to run your fan for at least 20 minutes after showering, and an independent control would ensure that you aren’t wasting electricity needlessly.

Ductwork

It is important to have adequate ductwork in place when installing your new bathroom fan. Installation of a new bathroom exhaust fan gives you a great opportunity to ensure that the fan is exhausting properly. A fan should not exhaust to the attic space. This is simply shifting the moisture from one room to another. Make sure the fan exhausts to the outdoors.

Similarly, multiple twists and turns and long runs of ductwork reduce the efficiency of the fan itself. Keep the ductwork to the shortest, most direct route to the outdoors as possible. This will ensure that the fan is actually moving the CFM indicated by the manufacturer.

Summary of Bathroom Exhaust Fan Functions

You can have the nicest, most powerful exhaust fan on the market, but it won’t guarantee any improvement in your indoor air quality if it’s not used, and used properly. When exhausting your bathroom air after a shower or bath, keep the bathroom door ajar so that the exhausted foul air can be replaced with clean, fresh air.

If you have any doubts about properly sizing your bathroom exhaust fan to your bathroom and home, consult a local contractor, plumber or electrician. And always be sure to check in on the exhaust ductwork before signing off on an installation job.