To limit the probability that excessively noisy fans will lead to occupants disabling or not using fans, which could lead to inadequate ventilation, which could lead to negative effects on the air quality of indoor spaces, which could lead to harm to persons.
To exempt fans with less than 1 m of duct between themselves and unfinished basements, furnace rooms, utility rooms or attics from the sound ratings specified in Table 9.32.3.10.B., on the basis that people do not normally occupy such areas for lengthy periods and would therefore be unlikely to be disturbed by noisy fans.