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Heating & Cooling

Bathroom Fan Noise: How To Tell Before You Buy

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One of the many things I have had to learn at Home Depot involved translating fan noise ratings into something I was familiar with.  Until I started selling bath fans, I was only familiar with sound measured in decibels, (dB).  30dB equates to a nice quiet room or the noise level of a modern refrigerator in an otherwise quiet kitchen.  Normal conversation without shouting is roughly 50dB.  Heavy truck traffic going by or many lawn mowers can put out 90dB.  Using a chain saw running wide open can scream at 110dB, as can using a jackhammer.  Sound pressure levels in dB can be easily measured using calibrated microphones.


What are Sones?



Bath fans are not rated in db, but in sones.

Just like dB, a sone is a measure of sound level.  There is a mathematical relationship between sones and dB, which not only takes into account the sound pressure level, but the sound frequency as well.  In addition, much like you can measure temperature in degrees Fahrenheit, Celsius or Kelvin, the scale for sones is different.  The idea here is to use a scale that more accurately identifies how loud a sound is perceived, and provides simple comparisons to other sound levels.


For a bath fan, the sone scale starts at zero, and goes up to about 6.  Zero represents the threshold of audibility.  The quietest fans available will be rated around 0.3.  A sone value of 1 will be a quiet fan that, while you can hear it, is more like background noise.  Think in terms of that kitchen refrigerator.  As the sone scale increases, each whole number increase doubles the perceived noise level.  A fan with a rating of 2 sones will sound twice as loud as a 1 sone fan.  A 4 sone fan will sound 4 times as loud as a one sone fan.  There are fans, typically bought for economy purposes and installed in apartments and motels that are rated 5.5 to 6 sones.  These fans are loud. 


Cubic Feet Minute (CFM)


So besides loudness, the other important rating for bath fans will be how much air they can move.  This is rated in cubic feet per minute, (cfm).  A basic rule of thumb is to get a fan that can move 1 cfm for every square feet of bathroom floor.  This is a minimum, and in humid climates you will want to go somewhat higher in airflow.  To move more air, a fan can either be speeded up, making it noisier, or made larger which costs more.  Those are the prime trade-offs involved.



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Posted 2015-04-07T20:24:04+0000  by Chris_HD_CHI Chris_HD_CHI