Abstract In the presented work the mathematical expressions for free outlet of turbulent streams are applied to solve fluid flowing in the working space of tunnel kilns. It is impossible to form 3D models of energy exchange processes and adequate temperature fields in a charge without the successful resolving of the problem. The elaborated methodology as well as the algorithm for determination of fluid flowing and circulating amounts allow to deal with heat exchange by conduction, convection and radiation without devaluating the obtained results the way that the essential conditions are neglecting due to the problem solvability. Because of the limited publication extent the solution is only focused on the spaces without fuel supply by burners. The presented solution is based on determination of the turbulent streams active surface (Fig.5), the equations (15 - 17), and the adequate amounts of air sucking up from the ambient, the equations (21 - 25). The amount of the circulating medium is given by the equations (30 - 33), and the complex view of the flowing is described in Fig.6. It is possible to apply the methodology and algorithms to various situations of charge loading in the tunnel kilns. The presented solution and algorithms make a basis for determination of fluid flowing and circulating amounts and this way prepare conditions for formation of adequate 3D models.