A bathroom fan can reach a sound volume level of above four sones, which is a measurement unit that correlates to how sound is perceived by people. At four sones, a bathroom fan's sound can be considered to be a nuisance, leading to reduced usage.
More energy efficient models of bathroom fans, such as those rated by the Energy Star program, typically have a maximum sound level of between two to three sones. The size of the bathroom fan used contributes to the maximum limit of sound it can generate. A quiet bathroom fan must have a sound volume level of under 2 sones.