Abstract: A control for the fuel input to a once-through boiler connected to supply steam through a throttle valve to a turbine-generator so that the rate of energy delivery to the boiler matches the rate of energy demand on the boiler as represented by demand signal. The fuel control involves comparing a demand signal indicative of the desired energy output rate for boiler with a signal indicative of the heat released to the furnace of the boiler and controlling the fuel input rate with a proportional and integral controller so that the fuel feed rate, such as coal feeder speed, is controlled so as to bring the signals into equality. The heat release signal is obtained by first calculating a lagged value of a quantity which corresponds to boiler output, such as steam flow or turbine first stage pressure, divided by fuel feed rate, such as feeder speed. That lagged quantity is then multiplied by a quantity corresponding to the value of the fuel feed rate.