Results of seasonal experimental investigations of natural draft in the potash mines after main fan stoppage are presented and analyzed. Underground mines with equal top elevations are considered. Three modes of natural ventilation depending on the season are determined: flow-through, local and convective ventilation modes. The mathematical model of unsteady heat exchange between mine air, shaft support and rock mass is proposed. This model allows prediction of natural draft intensity for flow-through ventilation mode. Also using system of linear convection equations we formulate natural ventilation stability criterion in case of convective natural ventilation mode for mine shafts after main fan stoppage. Formulated criterion based on Rayleigh number allows prediction of convective ventilation mode formation in shafts. (C) 2015 Elsevier Ltd. All rights reserved.