Detecting a fouled air filter in a computer equipment enclosure that includes an air filter, a supply plenum connecting the air filter and the computer equipment enclosure, a fan operating at a current fan speed, and a filter monitoring module connected for data communications to a management module. Detecting a fouled air filter according to embodiments of the present invention includes calculating, by the filter monitoring module, a pressure differential across the air filter; determining, for the current fan speed by the filter monitoring module in dependence upon a pressure differential profile for the air filter, whether the calculated pressure differential across the air filter exceeds a predetermined threshold value; and if the calculated pressure differential across the air filter exceeds the predetermined threshold value, reporting, by the filter monitoring module to the management module, that the calculated pressure differential across the air filter exceeds the predetermined threshold value.