This study presents a detailed method to estimate the thermal load of an articulated electric urban bus. Thermal load, which consists of solar, metabolic, ambient and ventilation heat loads, is estimated hourly for a one year period. A mathematical model takes into account the hourly passenger occupancy rate, hourly weather condition of the line and hourly solar loads as input and predicts the heat load accordingly. In order to determine the importance and contribution of each thermal load, all loads are calculated individually. Calculations are made for each hour of a year in order to observe the change of the contribution of each load in time. With the proposed method, the thermal load of an electric bus can be predicted in the system design phase and the HVAC system of the bus can be selected accordingly.