Abstract: A method for controlling a steam boiler or oil heater for maximum fuel efficiency by systematically finding the most fuel-efficient combination of input control values. A characteristic multi-dimensional look-up table is created by temporarily operating the process at all the possible functional combined settings of a plurality of input operators and recording for each combination of settings the resulting output values of a plurality of process parameters, for example, steam flow, steam pressure, and exhaust composition. Input combinations resulting in either non-functional process or unacceptable output values are eliminated. Steam flow rate is the primary output control parameter. A selected value of steam flow rate is the primary control setpoint for the process. If several combinations of input values can cause the process to meet the primary control setpoint, the combination using the minimum fuel flow is selected as optimal.