When you think of ventilation you may picture annoying fans that rattle your ears in the kitchen or bathroom. Fortunately, there are many quiet fans on the market that do an excellent job without all the noise.
Sound levels are measured in sones. The higher the sone level, the noisier the fan. Buy as quiet a fan as you can afford. For a fan to work, it has to get turned on, and it won't if it's noisy.
Spot fans are typically rated at 3 to 4 sones, though some can be quite a bit louder. Fans rated at 1.5 sones are very quiet, and low-capacity fans rated as low as 0.5 to 1 sones are nearly inaudible.
Since central ventilating fans run for extended periods of time, they should be no louder than 1.5 sones if they are mounted in the living space. The sone rating is not as important with remote-mounted fans, since you don't hear much of the fan noise inside the house. However, make sure that the fan is well secured so that it doesn't vibrate.
The way a fan is installed will affect its noise level. A low-sone fan attached to a duct that twists and turns, or is kinked or too small, will be just as noisy as the noisiest model.
Consider the quality of the fan's sound, too. Different sound frequencies produce different tones, even at the same sone level. Try to listen to the fan yourself before you buy it, to make sure that it's acceptable.
Excerpted from No-Regrets Remodeling by Home Energy (1997)