Natural ventilation is always an attractive topic in civil engineering. The attractiveness of natural ventilation comes from the potential reduction in energy consumption for the purposes of keeping the building atmosphere habitable. Nowadays with the development of super-computers, scientists have been applying theory of Computational Fluid Dynamics (CFD) in calculating and simulating flow fields in order to assess the ventilation characteristics of a given building. For simulation engineers, it is important that those CFD simulations generate reliable results at reasonable computational costs. The main purpose of this work is to investigate the performance of Ansys Fluent and OpenFOAM in terms of accuracy and computational expense for simulations of natural ventilation. The results in this paper shows that the outcomes of two softwares are similar and it should be noted that OpenFOAM is completely free distribution and the flexibility it offers allow the development of specific solvers by the user, which can be integrated with already existing tools