Circulating heating of fuel oil in railway tanks is performed, as a rule, with the help of saturated steam by preparing a heating flow of fuel oil with a temperature of about 80...90°C. For the operation services of fuel oil storages, it is interesting to consider replacing steam with hot water. The behavior of the existing system of circulating heating of fuel oil of M100 brand when changing the heating medium for the heater of fuel oil flow in the form of a plate heat exchanger is considered. The initial temperature of hot water is assumed to be equal to the design temperature of 115°C in the steam-fuel heat exchanger. The values of the thermal capacity of the heater flow of fuel oil, fuel oil consumption, flow rate and the temperature of the heating water flow at the outlet of the heat exchanger are defined depending on the temperature of the heated fuel oil in the range of 80...90°C. Reducing the temperature of fuel oil at the outlet of the heat exchanger from 90 to 80°C allows to increase its capacity by 30.1%, that is, to accelerate the heating of fuel oil in the tank and reduce the time of its discharge.