Abstract: An apparatus for mixing air streams in a duct or plenum of a heating, ventilating or air conditioning system is within a rectangular frame and comprises a centrally located square solid sided pyramid shaped deflector surrounded by four sets of air directing vanes, two long sets and two short sets, in rectangular apertures. The vanes divide oncoming air streams which pass through the rectangular apertures, along the vane's curved cross-sections, and are discharged at the vane's discharge angle toward the base of the pyramid shaped deflector. The pyramid shaped deflector divides the remaining oncoming air streams along each of its solid sides and directs the air streams into the mixing region. The divided air streams interface and mix in a region located around the pyramid shaped deflector's base to evenly temper air streams in a heating, ventilating or air conditioning system and distribute the mixed air uniformly across the downstream plenum or duct.