Purposes of a Bathroom Fan


A bathroom fan is an important part of every bathroom in the house. You may think that its only purpose is to exhaust smelly air from the room, but in fact, its actual design purpose is to remove warm, moist air from the interior of the bathroom to the outdoors. This warm, moist air not only encourages mold growth but also can cause damage to a bathroom. If yours doesn’t have an exhaust fan and it smells musty, it’s likely you need to install a fan. In fact, local building codes usually require that you install a fan that is sized to the specific area of your bathroom. ASHRAE 62.2 is a residential ventilation standard developed and maintained by the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) for more than 20 years. The ASHRAE 62.2 standard was developed in response to concerns of increasing levels of indoor contaminants and mold growth in residential buildings.


Definition -- a bathroom exhaust fan is a mechanical ventilation device that moves contaminated and/or moisture-laden air outside via ducting. By drawing out moisture, odor, and fumes from within the bathroom to the outdoors the air quality within the bathroom improves.


Potential Problems Without Bathroom Exhaust Fans


Without a bathroom fan, bathrooms are susceptible to excessive moisture buildup that increases the chances of damaging bathrooms and bathroom fixtures. Warm, humid air, caused by running hot water for baths and showers, is a perfect environment for mold, mildew and microorganism growth. High moisture in rooms can also break down materials like drywall, paint, and trim, not to mention the entrance door. For a safe, healthy bathroom, ventilate.


Bathroom Exhaust Fan Choices


Bathroom fans vary in styles and colors. They sometimes come complete with a light and sometimes even a heater option. They are usually controlled by either a single-pole switch or a wall-mounted timer. Placement of your bathroom fan varies on your preferred position. You may want the fan either over the shower, the toilet or possibly in the center of the room.


Bathroom Exhaust Fan Tips


Be sure that the dust flapper is installed properly to close when the fan is not in use. This keeps the cold air from the outside from filtering back into the bathroom. In fact, the duct should be insulated with insulation to keep condensation from building up from the difference of temperature between the inside and outside air temperatures.

How a Bathroom Exhaust Fan Works

The air is drawn out of the bathroom from an enclosure and extracted via a fan. The fan pushes air out through a duct that is attached to the fan enclosure to a weather resistant termination outside of the house. This termination is cut into a wall, soffit or the roof and attaches with screws and sealant. Properly sized insulated duct is used to connect the fan enclosure and the termination to safely carry the unwanted air outside.

Bathroom Ventilation Minimum Requirements and Recommendations

  • Less than 50 sq. ft. / 50 CFM
  • 50-100 sq. ft. / 1 CFM per sq. ft.
  • Install a bathroom vent fan in an enclosed toilet room.
  • Allow an air gap below the entrance door for required makeup air
  • Install wet location approved bathroom vent fans over the shower or tub
  • Rooms with ceiling heights over 8' may require additional venting
  • Choose quality bathroom vent fans based on CFM and noise level ratings for each
  • Suggested bathroom fan noise ratings of 1.0 or less are the best choice