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Do I Need a Bathroom Exhaust Fan?

What Does a Bathroom Exhaust Fan Do? 

Despite the hypothetical alternative of venting out your bathroom with an open window, all bathrooms require a bathroom exhaust fan for ventilation. 

If you don’t have or use proper ventilation in your bathroom when you are running water for long periods of time, the paint and infrastructure such as drywall and wooden supports will begin to decay. The paint will peel, mold will grow, and materials will start to rot and decompose. Although they sell mold-resistant paints for the bathroom, they should be used to supplement your protection, not as the sole prophylactic. A ventilation fan is also important when you are cleaning. The fumes from cleaning products can become toxic and overwhelming. In addition, when you have all the humidity building up in your bathroom, it will start to smell dank like a wet dog from the mildew and bacteria thrive.

bathroom exhaust fan

A Bathroom Exhaust Fan Improves Indoor Air Quality


The ventilation in your bathroom solves a myriad of potential problems in one shot, these are the most common reasons you should have a bathroom exhaust fan

  • Comfort:  As the warmer months approach, be sure to utilize your bathroom exhaust fan to help circulate the air, keeping you feeling fresh, cool and clean.
  • Prevent Mold Growth: Mold and mildew are not only unsightly but can cause damage to bathroom surfaces. Shower curtains can get mildew patches, towels can become smelly, and countertops will need more frequent cleaning. Your bathroom ceiling may also develop mildew without a fan. An exhaust fan can eliminate the moisture in the air and keep your bathroom dry.
  • Aesthetics: Peeling paint or wallpaper can be caused by excess moisture in enclosed or smaller spaces. Wood floors and doors can also be damaged by humidity. Using an exhaust fan to pull out the water in the air can help eliminate damage to your bathroom walls and floors.
  • Eliminate Odors: Bathroom fans can help get rid of foul smells more quickly. Exhaust fans work efficiently to keep your bathroom fresh and free from bad odors, smells and common bathroom scents by pulling the unpleasant aromas out.
  • Efficiency: While a hot shower may be just what you need to begin your day, stepping out into a hazy bathroom with fogged-up mirrors when you need to get ready in a hurry isn’t ideal. An exhaust fan can help clear the air in the bathroom quickly and efficiently, so you’re able to get on with your day.

Is opening a window better than a bathroom exhaust fan?

An open window simply doesn’t compete with a fan. If you leave your window open when it is raining, it will become more humid in the bathroom. If you leave it open when it is cold out, you are throwing money out the window and will see an increase on your heating bill. Although an open window is a nice feature when it is springtime and everything is wonderful outside, 90 percent of the time you won’t have the courage to open that window when you are in the bathroom.


Bathroom Exhaust Fan Size Guide

Choosing a bathroom exhaust fan that’s properly sized for your bathroom is something a Dean’s HVAC professional will be able to help you determine. The bigger the bathroom, the higher the CFM rating you’ll need. CFM stands for Cubic Feet per Minute.  A fan should have a CFM rating high enough to replace the air in your bathroom at a rate of eight times per hour.

For bathrooms between 50 and 100 square feet, estimate 1 CFM per square foot of floor space. For smaller bathrooms (less than 50 sq. feet), 50 CFM. For larger than 100 square feet, you have to tally the CRM requirement for each bathroom fixture to estimate your needs. Add 50 CFM for each toilet, tub or shower. And 100 CFM for jetted tubs.

The bigger your bathroom, the higher the CFM rating you’ll require.


The formula used to determine the CFM 

Length x Width x Height x 0.13 = Minimum CFM rating

Most fans will be rated from 50 to 110 CFM.

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