This paper aims at predicting the airflow patterns in a rectangular chamber under different inflow air speeds. This study employs a finite difference method with uniform single zone Cartesian grid to predict these airflow patterns. The governing equations are solved using an explicit MacCormack code developed by the author with forward and backward differences for predictor and corrector steps respectively. Special attention is paid to the boundary conditions that are strongly affected by air speed and openings. To stabilize the solution, a dissipation term is applied as a damping function to prevent divergence. Computations have been made on an isolated chamber of various rectangular shapes (i.e., different aspect ratios) and different inflow velocity profiles (i.e., different ventilation rates). Moreover, five different exhaust vent positions are considered. The locations of these outlet vents are on the left side wall as well as on the right side wall. This means that five different kinds of air diffusion models are studied. Fine and coarse grids are also considered for the analysis of patterns. Three grid distributions are studied for this purpose. The current algorithm has been successfully used for solving very low Mach number flows. This work is concerned with the steady state two-dimensional isothermal flow. A complete computed field is presented and discussed using an air flow velocity vector, streamlines and velocity ratios. The prediction of air movement and airflow distribution inside the chambers has been investigated. Prediction of the velocity fields as well as the primary recirculation of indoor airflow showed anticipated results. The effects of ventilation inlet/outlet arrangements on air movement have been investigated. In the case of low-speed inflow, flow separation after the inlet and before the outlet(s) of the chamber has been captured using both the fine and coarse grids. In case of high-speed flow, only one big circulation has been captured.