AirKing Lasko B-Air Blue-dri

Anatomy of Exhaust Fans

Exhaust fans play a pivotal roll in maintaining the indoor air quality of our homes. Utilizing them decreases contaminates, reduces moisture and makes our homes healthier to live in. So how do exhaust fans work?

Having an understanding of how exhaust fans or as they are sometimes called – bath fans work is an important component to making sure they are utilized correctly. The basic principle of an exhaust fan is to take the “bad” air inside your living space and move it (exhaust it) out. That air is then replaced with fresh air. It is a fairly simple concept.

The exhaust fan’s main component is a blower of some type. Lower end units will utilize a fan blade that looks similar to a typical portable fan. Higher end units will utilize a blower wheel or as some people refer to it, a squirrel cage. Blower wheels generally are able to produce more ventilation at a quieter sound level. In either case the wheel or blades turn and generate airflow that is directed through the fan’s duct collar.

The next part of the exhaust fan is the duct collar. Exhaust fans must be ducted to the outdoors and run through ducting in the home to either a wall cap or a roof cap. While these components are not necessarily part of the fan, they are integral components that are required. The duct collar of the fan is connected to the ducting from the home. Ducting can range from 3 inches to 6 inches in typical residential homes. More and more new construction is moving to 6 inch ducting as it provides better airflow with less resistance. It is important to match the ducting size to the size of the exhaust fan. For instance if you have 4 inch ducting but have a 6 inch ducted exhaust fan you will need to reduce the ducting down to fit. This will make the fan work harder, reduce the airflow and increase the sound level.

A second part of the duct collar is the backdraft damper. This is a flap that closes to prevent drafts from coming back into the home. Backdraft dampers are usually either gravity closing or spring loaded. The way they work is when the fan is operating and blowing air out of the collar the force of the air opens the damper. Once the unit is shut off the damper will either “fall” down on gravity type dampers or close with spring-loaded dampers, sealing off the ducting.

The next component of an exhaust fan is the housing. The housing holds everything together and is what is installed into the ceiling. Housings come in many different sizes and are installed in different ways. Common installations include hanger bars that slide into a channel on the housing and then extend out to connect to the ceiling joists. A second mounting type is mounting tabs. These are tabs on the housing that install directly to the ceiling joist. Other mounting types are ones such as with the Air King BFQ series that have a snap-in bracket.

So far all the components we discussed are ones you won’t see once the fan is installed. The one that you will see is the grill. Like housings, grills come in all different sizes and shapes. The grill has a few functions. First is to cover up and protect all the inter workings of the fan. Second is to be aesthetically pleasing – no one wants an ugly hole in their ceiling. Lastly the grill provides a balance of décor and function as it needs to be able to allow enough air to come into the fan without restricting that air.

These are the main components of an exhaust fan. In addition some fans will have extra features like a light, heater function, humidity sensor, motion sensor and more. For more information about the exhaust fans available through Air King utilize the exhaust fans tab at the top of the page.

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