In the not so distance past, there was no reason to exhaust air from your home using mechanical means.  With no air barriers, little insulation & leaky single pane windows, there was little to stop air moving freely in & out of the house.  Air was exchanged at sufficient rates to ensure minimal indoor air pollutants & large capacity furnaces literally cooked the house free of any moisture or humidity.  More

current homes have been built with saving money & fuel in mind.  These tighter homes do not allow enough air exchange & allow moisture & high humidity to remain in the home.  Although there are currently better ways vent homes (Heat Recovery Ventilators or HRVs, which I will cover in a later article), the most common method still are simple fans.

The majority of homes currently have exhaust fans in the bathrooms, either originally installed or retro fitted during a renovation.  Virtually all kitchens have hood fans & there is good reason for both.  As homes get built with vapour barriers, moisture barriers, more insulation in the wall/attic space & double pane windows, it is now essential that we have use of some mechanical means to remove excess humidity from our homes.

Importance of Kitchen & Bathroom Fans

During the cold winter months when opening windows & doors is not an option, using your bathroom & kitchen fans are important means of removing excess moisture & help improve your overall air quality in your home.

  • Bathroom fans should be running during a shower as well as for at least 20 minutes afterwards.  Although having a window open during a shower is helpful, it is not nearly as efficient in removing moisture as a fan.
  • Kitchen fans should be used whenever you are cooking on your stove or cooktop.  This will not only remove excess moisture, it will also remove some of the cooking odours.
  • Ensure that both kitchen & bathroom fans are vented to the outdoors, not into the attic space.

It is note worthy that recently it is not  uncommon that high velocity hood fans are installed without consideration of the overall air needed to allow other gas burning appliances in the home to operate safely.  Before installing such a fan, consult a HVAC (Heating, Ventilation, Air Conditioning) technician.

Fans need to be cleaned.  The movement of the fan creates static electricity that attracts dust and can quickly gather enough to significantly reduce the fan’s effectiveness.  For kitchen fans, grease accumulates & needs to be cleaned to prevent a chance of fire.

Types of Fans

  • impeller fans are the most common in bathrooms.  They are efficient in creating the draft needed to remove moisture from the room
  • blower fans are often used in kitchen hood fans.  They are more easily cleaned of grease
  • inline fans are generally more expensive but are very quiet due to the fan being installed in the attic space often close to the roof.

How to Choose the Right Bathroom Fan.  What Should I Look For?

There are two main issues to look at when choosing a bathroom fan,

1.  How Big of a Fan do I Need?

The amount of air a fan moves is measured in CFM (Cubic Feet Per Minute).

1.  Find the volume (cu. ft.) of the bathroom. Volume = length × width × height

Example: Volume of the room = 10 × 6 × 8 = 480 cu. ft

2.  Find the CFM (cu. ft. per minute). Volume (cu. ft.) ÷ 7.5

Example: CFM = 480 cu. ft. ÷ 7.5 = 64 CFM 

3.  This CFM is the minimum airflow required to achieve 8 air exchanges per hour

In this example you would only purchase a fan that has a CFM listed on the box of 64 or greater.

A Simpler Method

The average bathroom tends to be 100 sq. ft. or less.   If this is the case then you can  simply use a fan that is rated as 1 CFM per sq. ft., with a minimum CFM of 50.  If there is no fan with the same CFM, buy the next bigger.

The vent pipe leading to the exterior should be as short & as direct as possible as it has an effect on the CFM needed.

 2.  How Noisy is the Fan?

The following table can give you an idea of level sound you’ll get with different fans.  The level of sound is measured in Sones.  I would recommend not buying a fan rated higher than 3 sones as the amount a fan is used is often inversely proportionate to how loud it is.

                                              Background Sound Level          Typical Sones               Comfort Level

Rustling Trees                                    0.5                                    Noise Free

Evening Outdoors In Suburbs                       1                                       Noise Free

Open Office                                  1.5 to 2               Comfortable Verbal Conversation

TV & Radio                                     3 to 4                Comfortable Verbal Conversation

Traffic Noise                                   5 to 8                    Noticeable Background Noise


                         For more information about this or a home related topic, please don’t hesitate to contact me.

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