A chimney system is combined of two heated plates with adiabatic extension. The numerical analysis of the chimney system is carried out to clarify the performance of the free convection heat transfer and the augmentation of mass flow rate (m•) for the tested parameters. A Computational fluid dynamic (CFD) software, ANSYS-FLUENT, is employed in this investigation. Itis found that there is good agreement between the numerical findings and the experimental data collected from the literature, as demonstrated by this validation. Two types of obstruction are used in the present investigation, which are rectangular and semi-circular. The two types are tested at different configurations. Results reveled that the obstructions reduce the velocity and form vortices, which led to the reduction of the mass flow rate. In addition, it is found that the highest (m• ) is achieved with the base case However, the semi-circular chimney found to achieve the highest among obstructions.