Bathroom Fans 101

Bathroom fans might not be the most glamorous topic, but it’s one of the most important when it comes to keeping your home free from mould and rot. Bathrooms are the primary sources of moisture in a house, and moisture is enemy #1. It can damage the structure, accelerate the decomposition of materials and it can attract pests. A good bathroom fan is hugely important in protecting your home against these dangers.

Bathroom Fans

What Is a CFM Number

CFM stands for cubic feet per minute and it tells you how much air the fan can circulate. A bathroom fan needs to be powerful enough to replace all the air in the room about eight times every hour, so before you buy you’ll need to calculate the size of your room in cubic feet and then determine the appropriate CFM number.

Calculating the CFM Number

Determine the volume of the bathroom by multiplying length by width by height, and dividing that number by 7.5 (if you need to replace the air eight times in an hour that equals every 7.5 minutes). This number will give you the appropriate CFM requirements (round up to the next standard fan model to be safe).

What is a Sones Rating

The sones rating of a fan indicates how much noise is associated with it. The lower the number (from zero to five), the quieter the fan. To put it in perspective, 4.0 is equal to the sound of average television noise; 3.0 is typical office noise; 1.0 is about the same as a refrigerator running; and 0.5 sones is the sound of rustling leaves*. For quiet bathroom ventilation (ie – if it’s attached to a bedroom) the fan should be rated at 1.0 sones or less.

Fans that have high CFM’s and low sones ratings are the most expensive, but given all the other expenses in a bathroom, it’s worth it to splurge on the best fan you can. They usually range from about $75 – $300 so it’s not a huge expense, relatively speaking. And let’s face it, the best ROI will be achieved when you buy the best fan for the room. It’s that simple.

Using Your Bathroom Fan

Even the best fan is no good if you don’t use it. Some people prefer to have it tied into the overhead lighting so that every time the light is turned on so is the fan. But in this case you need to remember to turn on the light even if the bathroom is well lit by natural light during the day. You also have to be comfortable leaving it on after you’ve left the room while the moisture clears. Because of these issues many people are now turning to timers. When the fan is on a timer you can set it to run for a specific period of time and it can be on a separate switch from the light.

Bathroom Fan

Bathroom fans definitely aren’t the most fun part of a bathroom remodel, but they’re very important when it comes to protecting your home and maintaining it’s value. When you’re renovating your bathroom don’t forget this very important element.



*Numbers courtesy of the Home Ventilating Institute

Photos courtesy of Skit inc.

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