There are numerous reasons why fans may fail to perform as specified, but first it is important to understand what defines acceptable performance. According to Air Movement and Control Association (AMCA) Publication 200, a fan installed in a ventilation system should expect a tolerance of +/- 7.5 percent for airflow (cfm). In other words, a fan which produces 1,000 cfm in a lab environment should provide a volume flow rate of 925 to 1,075 cfm when installed in a properly designed ventilation system. Volume flow rates which fall below this range are typically the result of variances in system static pressure or mechanical problems with the fan.
Common symptoms include: