Ventilation by Exhaust Fans

An exhaust fan is a mechanical ventilation device that helps to draw out stale and impure air from your home and bring in fresh air, thereby improving the quality of indoor air. Exhaust fans are typically ducted to the exteriors of your house, through which bad indoor air can effectively be removed from your living space.

Exhaust fans are classified into various types, mainly depending on the type of mount and the location where you need to install the fans. The different types are:

1. Ceiling Mounted Exhaust Fans: As the name suggests, ceiling exhaust fans are those which are installed in the ceiling. Such fans expel stale air from your home upwards through the roof.  The fan is connected to ducting, which is exhausted outside the home via an external vent, like a roof cap or soffit exhaust vent.

2. Inline Exhaust Fans: Unlike ceiling exhaust fans that are installed directly into the ceiling, inline exhaust fans are typically mounted in-between ducting, hence the name inline fan. For instance, if you wanted to ventilate an area that did not have clearance or space for a ceiling mount fan, you would make use of inline exhaust fans to ventilate such areas. The exhaust fan would be placed in between the ductwork and the stale air would travel through the ducts and ultimately be expelled from your home.  Since inline fans are not mounted directly to the ceiling, they are very quiet.  When installing an inline fan, to reduce noise, we recommend using an insulated flex duct that is at least eight feet long from the intake port on the ceiling to the inline fan.
Inline exhaust fans are ideal for exhausting areas or rooms where you cannot, or do not wish to install the exhaust fan directly. Since these types of exhaust fans are mounted in remote areas, they are also referred to as remote mounted exhaust fans. Inline exhaust fans can either be single-port (exhausting from a single area) or multi-port (exhausting from multiple areas).

3. Wall Mounted Exhaust Fans: These exhaust fans are installed on walls. Since they are installed on exterior walls of the home and not on interior walls, the stale air has a direct route to the outside of your home and thus no duct work is required in installing these exhaust fans.

4. Combination Exhaust Fans: Exhaust fans are also available as combination units. You have the choice of a fan-light combination where the exhaust fan provides illumination as well, or heat-fan-light combination wherein you get a heater, light and ventilating fan all in a single device.

5. Exterior Remote Mounted Exhaust Fans: While most other exhaust fans are installed inside your home and push stale air out, exterior remote mounted fans are installed outside your home and pull out stale indoor air instead of pushing it out. The main benefit of these exhaust fans is that regardless of however noisy they are, most of the noise remains outside your home.

6. Kitchen Range Exhaust Fans: These fans are mounted inside the range hood over your kitchen stove. Such fans not only help to rid your kitchen of stale air but also help to expel bad odors and reduce moisture levels in your cooking area.
 
These several types of exhaust fans can be used for complete ventilation of your bilding including intermittent local ventilation for baths, kitchens, dryer rooms; continuous whole building ventilation, and for exhausting hard-to-air spaces such as crawl spaces, attics, and basements.

Exhaust fans are very effective at ventilating your home and other living spaces. Without proper ventilation, the air inside your home can get filled with harmful contaminants and disease causing pathogens.

Pollutants such as pesticides, harmful gases, smoke, pet dander, lead, asbestos, dust mites, paint fumes, grease etc get released into indoor air due to daily activities such as cooking, smoking, burning fuel, bathing, renovating etc. In addition to these pollutants, activities such as bathing, cooking, and washing also release excess moisture in the air and make indoor air extremely humid. If not ventilated adequately, these added pollutants and increased moisture levels can decrease the quality of indoor air greatly, thereby leading to various problems such as:

Health problems including asthma, allergies, nose bleeds, skin rashes, headaches, nausea, and other breathing disorders. In fact, according to the Environmental Protection Agency, a large percentage of the over 20 million annual asthma cases in the US alone can be attributed to bad indoor air quality.

- Split, warped and rotted furniture due to excess humidity.
- Cracked and peeling paint on the walls.
- Formation of fungus, mold spores, and mildew, which in turn lead to severe health problems.
 
Thus, by using exhaust fans to ventilate your building efficiently and completely, thereby improving indoor air quality, you can avoid of all these problems.

When sizing an exhaust fan that does not open directly to the outside but is ducted, it is important to ensure that the exhaust fan has the capability to move stale air throughout the duct and ultimately to the outside. Here, we first need to understand what static pressure and equivalent duct length is.

Inside every duct, there is a constant pressure being exerted at any point from all directions. When an exhaust fan moves air through the duct, the air counters resistance from this pressure which is known as static pressure. Thus, an exhaust fan has to have the ability to overcome the static pressure in a duct so as to effectively duct stale air to the outside of your home. This can be done by calculating the equivalent duct length of any duct.

Additional information can be found at the Canada Blower company web site http://canadablower.com/fans/index.html.

Susan Terlitski
Canadian Process Air Systems Designer
Canada Blower
http://canadablower.com/hvac/index.html
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