Nasal inspiration is important for maintaining the internal milieu of the lung, since ambient air is conditioned to nearly alveolar conditions (body temperature and fully saturated with water vapor) on reaching the nasopharynx. We conducted a two-dimensional computational study of transport phenomena in model transverse cross sections of the nasal cavity of normal and diseased human noses for inspiration under various ambient conditions. The results suggest that during breathing via the normal human nose there is ample time for heat and water exchange to enable equilibration to near intraalveolar conditions. A normal nose can maintain this equilibrium under extreme environments (e.g., hot/humid, cold/dry, cold/humid). The turbinates increase the rate of local heat and moisture transport by narrowing the passageways for air and by induction of laminar swirls downstream of the turbinate wall. However, abnormal blood supply or mucous generation may reduce the rate of heat or moisture flux into the inspired air, and thereby affect the efficacy of the process.