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Bathroom Exhaust Fans

Bathrooms are typically the most humid rooms in your home. Often bathrooms are small in size relative to the amount of moisture produced by its fixtures. All the concentrated moisture and humidity causes the potential for mold and mildew, which can affect your health, and the integrity of your home. Luckily, with the addition of a properly installed bathroom fan you can protect yourself and your home from any potential issues. Now you must be asking, how do you choose the right bathroom fan? Below we have outlined a list of important factors when it comes time to pick out and installing a bathroom fan.

Air Flow and CFM

Bathroom fans have varying air flow values, often measured in cubic feet per minute (cfm). To help you choose the optimal fan cfm for your bathroom, we have simplified things.

  1. Calculate your square footage (Area) of the bathroom. This is done by measuring the length (L) and multiplying it by the width(W). (LxW= Area). Include showers and bathtubs in your calculation as well.

  2. If you have a standard 8’ ceiling height, your bathroom fan should have 1.2 cfm for every square foot of floor space in your bathroom. (Areax1.2= Required cfm)

  3. For ceilings taller than 8’ in height, add an extra 20% (Required cfmx1.20= New required cfm.

Depending on your fixtures and usage, you may choose to invest in a larger fan to make sure you have enough cfm to clear the room in a timely manner. Extra fixture considerations would be, jacuzzi tubs, steam showers and laundry units.

Noise Level and Sones

Here in Ontario, fan noise is rated by a unit called sones. Sones is a scale that represents degrees of loudness. Without getting too technical, a rating of 0.5 to 1.2 sones means the fan is extremely quiet. A sones rating of 1.5 to 2.0 is fairly quiet . Fans rated in excess of 4.0 sones are considered to be noisy. Often bathroom fans with lower Sones are more expensive and highly rated compared to their noisy counterparts.

Proper usage and Options

Bathroom fans are a powerful tool for protecting your home. The biggest issues with bathroom fans are typically human error in day to day usage. Most homeowners do not use their bathroom fan as designed. It is not enough to have your fan on while showering, in fact The Home Ventilation Institute (HVI) recommends running the fan for at least 20 minutes after the shower has been used. We suggest cleaning and maintenance of the fan to be done at least once a month to prevent dust build up.

As technology has advanced homeowners have more options than ever before to enhance and maintain proper exhaust fan usage. The following are some options to consider when choosing your next bathroom fan. 1) Timer- This addition will allow the homeowner to choose the duration of the fan being on. Typically in increments of 5 minutes, this option is great for the forgetful type or who want to set it and forget it.

2) Motion sensor activation- this turns on the fan when someone enters the bathroom. Regardless of task, the fan will automatically activate and start removing moisture, odors and stale air. This option is great for kids as they may forget to turn the fan on while the bathroom is in use.

3) Humidity sensing- With this addition your bathroom fan automatically turn on when the unit detects high levels of humidity. This option is great for showers and spa rooms, but not ideal for powder rooms as the sensor does not detect odors.

Proper Venting

Bathroom fans are designed to pull in humid or stagnant air and exhaust it away. Most bathroom fans use a 4” wide flexible pipe, although some models can range from 3” to 6” in diameter. It is important that your bathroom fan exhausts to the exterior of your home. We have seen many short cuts where bathroom fans are set up to exhaust into the space between ceiling joists or attic spaces. Venting this way will force excess moisture into the worst possible conditions; closed, dark spaces where humidity collects and helps mold to spread, damaging floors, walls and ceilings. An important part to the venting system is the damper. Dampers are flaps that help control air flow and help prevent backdrafts. Dampers are shut when the fan is off and will open up as it is turned on. Proper bathroom venting should always include 2 dampeners, one at the fan inlet (where the air first enters the pipe) and the other at the fan outlet(where the air is finally exhausted to the exterior). Another requirement for a worry free venting system is insulation. The Ontario Building Code (OBC) requires all venting running through uninsulated or non-temperature controlled space to be insulated. This insulation is often seen as a black sleeve that is pulled over the venting pipe. This sleeve is made with fiberglass insulation and thick plastic. The OBC also requires that the last 5’ of venting pipe, which meets the exterior wall, also be insulated. The insulation added to the venting pipe will help reduce the chance of condensation from forming on the pipe, which will further reduce the risk of mold and potential fan failure.


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