Maximum Recommended Sones for Bathroom Fans
Installed in bathrooms that do not have a window for ventilation, fans can reduce both odors and moisture. The units, rated on their ability to move air as well as their loudness, are not difficult to replace.
Available at building supply stores, fans have noise and airflow figures printed on the box, making it easy to select the proper unit for your bathroom.
A sone is a measurement of perceived loudness. The higher the number of sones, the louder the device is to the human ear. Normal conversation is 1 to 2 sones. Rustling leaves are about 0.5 sones, a refrigerator operates at 1 sone, a TV set playing at a comfortable level is about 4 sones, and a jackhammer is about 65 sones. Hearing damage can begin at 256 sones, but the human threshold of pain can be as high as 650 sones.
Ideal Sones for a Bathroom
Since the technology of bathroom fans allows some to operate at near-silent levels (less than 1 sone), the lowest number of sones is considered ideal. A very quiet fan, making just a soft whoosh sound, probably operates at 1 sone or less. The tradeoff for a quiet fan is cost: The lower the sones, the higher the fan's price tag. The obvious choice for a bathroom fan is one with the lowest number of sones, but the true number of concern is the highest acceptable sone level. Fans for small bathrooms should not exceed 2 sones, and fans for larger bathrooms should remain under 3 sones. Fans louder than 3 sones are unacceptable.
Most exhaust fans are rated by the Home Ventilating Institute based on their ability to exchange the air in a bathroom at least eight times per hour. Bathroom fans should be left on for 20 minutes to complete the task of refreshing the air and removing water vapor. The formula to correctly select a fan with the proper strength to remove air is to determine the room's volume (length x width x height), then divide the figure by 7.5 to get a sum. This is the necessary cubic feet per minute, or CFM, needed to exchange the air more than seven times an hour. New or replacement fans should meet or exceed the calculated CFM.
Tips for Installation
Even a low-sone fan can create vibration noise when improperly installed. Use screws when completing an installation, never nails. Nails have a tendency to vibrate loose and may lead to noise down the line. Use larger venting (4-inch) to decrease pressure on the fan and allow for quieter use. Vent lines should have gradual turns, never sharp turns.