Abstract: A novel plenum chamber and system for the mixing and subsequent distribution of two different fluids. In the preferred example the fluid is air and the chamber mixes fresh and recycled air proportionately and subsequently distributes the air stream through buildings, etc. The plenum chamber is in connection with an fresh air inlet duct and a recirculated air inlet duct at opposite ends, and an outlet duct along a third side. Louver panels divide the chamber into passages that are connected to one of the two intake ducts, the passages alternate being in connection with one or the other of the intake ducts so as to create a stratified mixture of air layers, alternating fresh layer, recirculated layer, etc. chambers. The outlet section is in connection with a distribution fan for dispersal to the rest of the building.