Abstract: A locomotive cab heating system having a plurality of separately actuated heating units housed in a supply air duct and connected to a microcontroller. Preferably, the system includes a high temperature shutdown thermostat. The microcontroller is equipped with memory storing a program that is configured to control the microcontroller to turn on and off a predetermined number of the heating units responsive to temperature readings received from the temperature sensor, thereby maintaining air temperature in the duct within a selected range, regardless of fan speed and air flow rate. By controlling the number of heating units in operation at any given time, the heating system of the present invention controls the heat delivered to a locomotive cab more effectively, thereby ensuring the comfort of the occupants of the cab. The locomotive cab heating system of the present invention is designed to be easily and inexpensively retrofitted to preexisting heating systems.