What is a sone?
When you start researching ventilation fans, you'll find the noise level is rated in sones. Most of us are more familiar with decibels. Decibels and sones use a different scale, but both start at zero.
The sone is a unit of how loud a sound is perceived. The sone scale is linear. That means doubling the perceived loudness doubles the sone value.
Normal talking a yard or so away from a person would be around 40 to 60 decibels, or 1 to 4 sones. A quiet library is about 30 decibels, city traffic inside the car is about 85 decibels. Hearing damage starts to occur around 90-95 decibels. A loud rock concert is around 110-115 decibels.
By comparison, 90 decibels is equal to about 32 sones.
Whole house ventilation fans designed for continuous running are supposed to operate at 1 sone or less. The thinking is, if they are louder than that people will turn them off and then will miss out on the benefits of continuous ventilation.
Broan's Ultra Green series of spot ventilation fans for bathrooms has a sone rating of <.3 sones, about the lowest that can realistically be measured. That means a fan does its job quietly in the background, removing moisture and odors from your home.
Bathroom fans and kitchen fans are louder than of course but they're designed to run for short periods for a specific purpose. You can turn them on and off at will. And they also move a lot more air in a short amount of time. Economy priced bathroom fans will have ratings anywhere from 1.5 to 6 or so.
Kitchen vent fans are available in the same range, from <0.3 sones for premium models to 6 or higher for economy versions.
A low sone rating is usually an indicator of high quality engineering and materials, but those quiet fans typically cost more than a louder fan.
Next time you're in a home store, test the difference. Like a lot of other things in your home, you get what you pay for.