This work describes a new approach to simulate the airflow and air-conditioning in the individual human nasal airways using voxel-based modeling with Cartesian structured grid. Computed tomography imaging scans of a healthy adult nose were used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulation of quiet restful inspiratory flow was then performed using meshes of varying refinement to determine the level of mesh refinement required to adequately resolve the flow and heat transfer. For meshes with a voxel pitch of 0.20 mm or less, the voxel model successfully reconstruct the realistic nasal structure and simulate the overall pressure drop and airflow temperature. The resultant streamlines and vorticity distributions reveal the characteristic flow structure in the nasal cavities, with high speed jet posterior to the nasal valve, recirculating flow that occupies the anterior part of the upper cavity, and low speed flow in the olfactory region. It was also found that the impinging jet plays an important role in the air-conditioning performance in the nasal cavities.