Fan airflow is rated using cubic feet per minute (CFM), we have tried to list below tips we've developed over our 20 years in the business to determine how much airflow you require.
Electronics Cabinet Rule of Thumb Formula:
Length * Width * Height * 4 = Required CFM
Please note that this is a rule of thumb, not a law. Other factors will include the outside ambient temperature, the level of electronic processing in the cabinet (# of devices), and the cabinet's circulation design.
The larger fan size will push more air for a given noise level. A larger blade surface area allows the fans to run slower for the same airflow as smaller faster running fans. The volume (normally measured in decibels--dBA) increases as the rotations per minute (RPM) increases. However, we have also noticed reliability and static pressure drop-offs on DC fans if they get too large. We normally recommend our 120mm (4.7") fan kits if space permits. We realized however that not everyone can use fit our kits which use 120mm fans so we do offer kits in 80mm, 92mm, and 140mm.