This work is a contribution to the improvement of the thermal and the dynamic fields of a natural convection indirect solar dryer, composed of a solar flat air heater and a drying chamber, intended for drying agricultural products and medicinal plants. We have studied the effects of size and position of the outlet on the distribution of air and temperature within the drying chamber, containing the figs as a product to be dried. To be more realistic, we have used a user defined function (UDF) subroutine written in [Formula: see text] to integrate the unsteady evolution of a day’s climate data in the Oujda region. This study was achieved by numerical simulations using the ANSYS FLUENT software, in order to optimize the distribution of air and temperature inside the drying chamber, and to choose the best outlet’s position and size for the best efficiency of the dryer. The results show that the optimal outlet position found is in the right corner with a size range of 0.07 to 0.15[Formula: see text]m. The effects of the position and size of the outlet on the air deflection along the trays were also presented and discussed.