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What is the Quietest Inline Fan?
In order to find a quiet inline fan, it helps to know the sone rating of the contenders. This rating is similar to a decibel rating, but using a scale that's meant only for fans. Manufacturers that want to market their fans as "quiet" will often print the rating for their equipment on the side of the box or in the specs. Notably, not all who do this actually have quiet fans. Therefore, it's important to actually read the rating instead of just assuming that its very presence indicates quietness.
Both sones and decibel ratings are sometimes used by fan makers, so if you don't see a statement that uses sones, look for a decibel rating instead. A rating of 1 or 2 sones is considered very quiet, and corresponds to between about 28 and 38 decibels. That's between the volume of a whisper and soft music.
Other Factors that Determine the Apparent Loudness of an Inline Fan
The ambient noise in the room greatly affects the perception of sound. A fan serving a room that has a few people talking will seem much quieter than one that's in a room that is otherwise pindrop-silent. Because of this, it's much more important to have a 4-inch inline fan quiet bathroom ventilation fan than it is to have a quiet fan in a busy work area.
Noise perception is also affected by the mental and physical state of those listening. At least for some people, stress, tiredness, and illness can all make noises seem louder and more annoying. Therefore, doctor's offices, hospital rooms, and other locations that are likely to draw people who are stressed should be outfitted with inline fans that have the lowest sones ratings. Even the testing areas at universities can benefit from extra-quiet ventilation due to the stress associated with exams.
You may find that even if you start with a quiet inline duct fan, you end up hearing much more noise than you expect. This is typically due to vibrations in the ductwork itself. Some ducts are put in place very loosely, and this can allow them to resonate with the fan's vibration. Then, the sound of the vibrating ducts is amplified along the ducts' length, making the fan seem louder than it is. In this case, the solution is to use insulation or a similar material to stop the ducts from vibrating.
The possibility of the ducts vibrating can be reduced by choosing a low-turbulence fan. These send out air in a smooth, linear fashion, thereby reducing the amount of air that bounces off of the insides of the ductwork.
Other Things to Keep in Mind
As with any equipment purchase, it's important to look for things like a long warranty and good manufacturer reputation. Also, for a fan, it's important to be sure that the rated airflow is high enough. These steps will help ensure that you get a fan that will not only meet all of your needs, but do so for a long time.
At Industrial Fans Direct, we carry a wide selection of in-line duct fans to meet any need. Look here first when you need to add ventilation.