The objective of the paper is a proposal of a quick start of the steam boiler from the cold state. Fuel consumption rate necessary for heating the evaporator from initial temperature to a predetermined temperature was determined using a transient mathematical model of the boiler evaporator developed in the paper. The model takes into account that at the beginning of the evaporator water is heated without steam generation and then after reaching the saturation temperature the boiling process is started and steam is produced. The mathematical model of the evaporator was verified experimentally. Heating of the evaporator is carried out with a maximum temperature change rate due to the maximum circumferential stress occurring at the edge of the drum-downcomer junction. After determining the optimum fluid temperature the pressure can easily be determined because the pressure of the saturated steam is a function of temperature. Using mathematical models of the evaporator and the combustion chamber the mass flow rate of the fuel ensuring optimum drum heating was calculated. The mass of heavy oil consumed during optimum warm-up of the drum was also calculated. (C) 2015 Published by Elsevier Ltd.