Computational Fluid Dynamics (CFD) is an important tool in building HVAC design and indoor environment modeling, but the computing speed of a CFD has been becoming a key factor in preventing its application. The grid independent solution of a CFD simulation is required by almost all scientific investigation but has significant requirement on computing time and hardware. Using coarse grid is an option to solve this problem. Coarse grid CFD can provide faster and informative result but the credibility is always questioned due to the unknown error scale coarse grid brings. This research investigates the possibility of applying coarse grid to typical indoor environment modeling. An optimized coarse grid balancing the trade-off between the grid resolution and simulation accuracy is recommended.