in a system for rapid air temperature modification in a recycling oven using hot air impingement for cooking , a fraction of the recycling air may be made to selectively bypass the heat exchanger , thereby to rapidly achieve reduced cook chamber temperatures , as desired by the user . the system includes a shell configured and dimensioned to receive a stream of air through an inlet and to discharge a stream of air through an outlet . the shell is further configured to provide independent first and second paths of travel to guide independent streams of air passing between the inlet and outlet of the shell . the first path houses heating means so that all air passing through this first path will be conditioned by the heating means . the second path has no heating means and merely permits unimpeded passage of the stream of air through the shell . a mixing space or chamber exists just prior to the outlet of the shell , wherein the air leaving the first path is mixed with the air leaving the second path , so that a single , common thermally - uniform stream of air is created prior to this united stream passing through the outlet and into the cooking chamber .