Increasing the horsepower of a fan of any diameter will increase the noise level created by that fan. A proper balance needs to be achieved between fan diameter, horsepower, noise level and the even distribution of air over the area to be ventilated when considering the size and quantity of fans required for a defined area.
When selecting the fan diameter, whether it is a roof or wall fan, consideration should be given to the existing framing plan of the building. Using a fan diameter that will fit between the existing framing members of the building is important in order to avoid unnecessary installation costs. Ventilation equipment is manufactured in various sizes to accommodate varying building framing schemes, and choosing a fan diameter which best fits the existing framing of the building will make the installation less complicated.
The noise level created by the ventilation equipment to be installed is the next factor that needs consideration. The noise level must be maintained at an acceptable level when determining horsepower. Usually the noise level the employees will be exposed to should be kept below 70 decibels. The noise rating in decibels decreases as the distance from the source increases. The further the fans are from the employees, such as fans mounted in the roof of a building with a high ceiling height, the less they will be affected by the noise the roof fan is creating.
For a comparison to common noise levels, a noise level in the 80 dba range is annoying, in the 90 dba range it's very annoying and will create hearing damage after eight hours of exposure.
A requirement in the design of any good ventilation system is the consideration of the noise level on the personnel that will be working in the same environment.