Model ESP is a revolutionary unhoused centrifugal fan designned for air handling applications. The fan pressurizes the plenum in which the fan operates and allows for ductwork to be directly connected to the plenum walls of the air handling unit. The plenum fan design saves space by eliminating the fan housing that can detract from system performance along with costly duct transitions. Plenum systems also work especially well with retrofit projects where limited space is a common problem