Abstract: 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 (heated) by the heating means. The second path has no heating means and merely permits unimpeded passage of the stream of air through the shell.