What Do Exhaust Fans Do?

Exhaust fans are used in bathrooms, kitchens, attics, utility rooms and other spaces in your home. The fans are designed to remove moisture, odors, smoke and other contaminants from interior air. The most popular exhaust fans are the motorized versions. As more homeowners have made their homes more energy-efficient, houses have become more insulated and airtight. This makes proper ventilation even more important. Inadequate ventilation and air flow can lead to moisture damage and unhealthy air quality.

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There are a wide variety sizes and types of exhaust fans, including ceiling mounted, wall mounted, inline exhaust, combination, and kitchen range hood exhaust fans. The typical ceiling mounted fan is installed in the ceiling, between two joists, in a space such as a bathroom or utility room. A wall-mounted fan is installed between two studs on an outside wall.

Inline exhaust fans are actually install in the ductwork and are usually used when there is sufficient space for installing a ceiling-mounted fan. A combination fan, which has light-fan-heat components, is usually found in bathrooms. Kitchen range hood exhaust helps vent smoke, grease and cooking odors to the exterior.

Some exhausts fan work very much like the traditional house fan; they are called propeller or axial fans. The fans can circulated a good amount of air and does not require a lot of pressure in order to operate. A centrifugal fan works like centrifugal water pumps, which forces the air out of the area.


The basic installation process consists of mounting the fan in a ceiling, wall or duct. The proper size ductwork must be run to provide ventilation to the outside. Connect the duct pipes to the exhaust port on the housing of the exhaust fan. Basic electrical skills are required to tap in to a nearby power source or run new wire to the unit. You will also have to connect the operating switch. The exhaust fan should always be vented to the outside.

Run the duct pipes through walls and/or ceilings and out the roof or through an exterior side wall. Do not terminate the duct in the attic, garage or crawl space. To do so may lead to expensive repair bills or compromise your health by creating and environment for mold and mildew.

Purchase the right size exhaust fan for the room it services. According to the Home Ventilating Institute (HVI) a fan should perform a specific number of air changes per hour (ACH). For example, the recommended ACH for bathrooms is eight. Kitchens have an ACH of 15 and other rooms have an ACH of six.

Buy the correct size fan for your space by the “cubic foot per minute” or CFM. Calculate the CFM for the fan you’ll need by multiplying the square footage of the bathroom by 1.1. So, if you have a 120 square foot bathroom, purchase a fan with a 132 or greater CFM.

For a kitchen range hood exhaust fan, you’ll need 100 CFM for each 10,000 BTU of the range. For example, if you have a range with a 60,000 BTU, purchase an exhaust fan with 600 CFM or greater capacity.


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