Means for regulating the operation of a steam-generating unit to produce steam at the required temperature. The temperature of steam is affected by the change in the relative heat absorption as load varies, by changes in ash or slag deposits on the heat-absorbing surface, by changes in fuel, by changes in the proportioning of fuel and combustion air, or by changes in feedwater temperature. Low steam temperature lowers the efficiency of the thermal cycle. However, high steam temperature, which increases thermal efficiency, is restricted by the strength and durability of materials used in superheaters. Control of steam temperature is, therefore, a matter of primary concern in the design of modern steam-generating units.