The PDI-HEF-1 is a 19" rack mounted crossflow blower to be used with our 6 in 1, 12 in 1 or any other rack mounted modulator systems in non-air conditioned environments. The PDI-HEF-1 utilizes a 10-3/4" aluminum impeller to move air in a 90 degree direction, from the bottom to the top of the modulator system. It is extremely effective.