The purpose of this study is to predict the safe storage height of coal stockpiles. To accomplish this, a one dimensional non -steady - state model with the effect of stockpile height approximated by a heat sink in the one dimensional energy equation has been developed. The model consists of conservation equations for oxygen, water vapour, inherent moisture of the coal, and energy for both gaseous and solid phases. The heat sink term taken from literature is based on an assumed sinusoidal variation in temperature in the vertical direction. Numerical solution of the model equations gives the time-dependent maximum temperature in the coal stockpile. The effect of stockpile height on the maximum temperature has been analysed parametrically for four different low-rank Turkish coals. When the safe storage time is specified, the critical height can be determined. By defining the storage time as three months, it has been found that these critical values varied between 0.85 and 1.8 m. depending on the liability of the coals to spontaneous heating.