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Clear the Air With A Bathroom Exhaust Fan

Q. I want to buy a quiet fan. Can you explain the way manufacturers rate their fans?

A.  Here's a brief primer on sound measurement for exhaust fans...

The phon is a basic measure of sound levels.  However, it is not a linear measurement.   40 phons is not twice as loud as 20 phons, it is four times as loud!  Needless to say, this is not the type of measurement I would call user friendly.  To make the system more understandable and useful for us normal folk (right), the sone system was developed. 40 phons equal 1 sone. A two sone sound is twice as loud as a one sone sound... three sones is three times as loud... etc.

To get a feeling for the relative volume of a sone, your average refrigerator with its motor chugging along is about one to two sones in loudness. Typical ceiling mount bathroom fans vary from 1.5 to 5 sones.  Some larger high volume ventilators can generate a whopping 10 sones, while so-called "inline" fans (more later) can appear to be almost noiseless... except for the whoosh of air into the vent!  All exhaust fans should have a sone rating on their box, which gives you a convenient way to compare the relative loudness of fan units.

Useful as this information can be, the testing done on the fans does not take into account the eccentricities of your home or the installation of your fan (or of the installer). Additional noise can be caused by vibration of the fan cover, the wiring, or even the ceiling itself.    To make comparison even more difficult, the higher velocity fan motors have a greater potential for vibration.  As a rule, the combination of a  more powerful fan motor and a larger turbine (fan blade) is the most quiet fan..  Less expensive fans using very fast fan motors with a small turbine are the noisiest fans.  Sure, they move lots of air, but really rock and roll when it comes to increased noise!

Don't be fooled by low sone ratings... look at the CFM rating, too!

This is a simple concept but easily overlooked when you're in a shopping frenzy. AND I KNOW SHOPPING FRENZY!! Two exhaust fans may have the same sone rating but move radically different volumes of air... the infamous CFM or cubic-feet-per-minute rating. A slow turning fan will always be quieter, but what good is it if you don't get enough air movement? So in your shopping, take a deep breath and decide on the CFM rating you need first (see the formula earlier in this article).  Then compare sone levels.  Your goal.... to purchase the quietest fan you can afford that can move the air you need!

The quietest and most powerful exhaust fans are the so-called "inline" fans. They mount in the attic, not on the ceiling, and are connected to a ceiling or wall register with flexible ducting. They don't vibrate the wall or ceiling since they are hung from the roof rafters, further decreasing the noise level.

Stop salivating, guys... inline fans are not for everyone or every home. They are all high air volume units, some with enough power to make your ears pop. And remember... all this air that is being pumped out of your home has to be replaced with non-environmentally controlled outside air... courtesy of Mother Nature. Whether winter or summer, your heating, AC and dehumidification bills will increase if you purchase too "macho" a fan for your real needs!

On the Web...

Many manufacturers have web sites that offer the vital statistics on their fans.   If you have narrowed your search to a specific brand or just want to see the range of products they build, these sites will help you focus on their best offerings! Two examples are Nutone and Broan at

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