Abstract: Recovery boiler wind boxes are upgraded by providing an air nozzle and damper installation where the nozzle crosses through the inside of the wind box. Air is channeled from the box into the nozzle by the damper. The nozzle is convergent and jets air into the boiler's combustion chamber. The typical boiler has a plurality of combustion air ports leading into the chamber. Modifying each air port by using the nozzle and damper installation creates a surrounding arrangement of air jets about the chamber which creates turbulent mixing in the boiler's furnace gases.