How Exhaust Fans Work

Consumer- and industrial-grade exhaust fans serve bathrooms, kitchens, factories and almost any other facility where occupants need to quickly evacuate fumes or odors. To accomplish their task, exhaust fans typically rely on an electric motor fed by an outside power source like commercial electricity or, in some cases, a battery. The user controls the flow of electricity through a toggle switch installed inline with the electrical wiring; when the user places the toggle switch in the "On" position, it completes a simple electrical circuit and sends power to the fan's electric motor. When the user no longer needs the exhaust fan's service, he can flip the switch to the "Off" position to interrupt the electrical flow and turn off the fan.

When a user turns an exhaust fan's switch to the "On" position, electricity flows to a powerful electric motor central to the fan's operations. Like most electric motors, an exhaust fan's motor uses the electricity's magnetic field to rotate a metal shaft. The magnetic force created by the electrical flow over copper wires inside the motor overcomes the inertial force of the fan's shaft and blades, and the fan begins to turn. Once the turning motor places the fan's shaft and blades into rotation, the angled surface of each blade slices through the air, collects stationary air and forces it to move in the direction, usually upward, of the exhaust vent.

Some exhaust fans are equipped with capacitors that regulate the flow of electricity to the electric motor. If the user selects a higher fan speed, the capacitors allow more electricity to flow through to the electric motor, and the motor spins faster. As the motor spins faster, the attached fan blades collect air more quickly and repeat their revolutions more frequently, forcing a higher volume of air through the exhaust pipe per unit of time. Depending on the fan model, the fan may have two, three or even five speeds that can evacuate varying volumes of air based on the user's needs.

When a user employs an exhaust fan to evacuate fumes or odors, the rotating fan blades collect the air containing the offensive particles and push them out of the facility. As the air leaves the facility, the fan can only point it in one direction, usually upward. In most applications, an exhaust fan directs air upward into a series of exhaust tubes that route the fumes or odors through a building's ceiling and into the outside environment. In some simpler applications, like factories and small bathrooms, exhaust fans reside in the structure's ceiling and simply push air from inside the facility directly to the outside.