A suboptimal control strategy to control heat treatment processes in a direct-fired batch type furnace is formulated. It minimizes deviations from a prescribed temporal load temperature profile and the energy input in terms of the fuel consumption. The control method requires a model for the heat transfer and combustion, which is described. Application of the method shows that the fuel input and heat transfer to the load can be controlled to maintain a specified instantaneous temperature. This is accomplished through a feedback loop that is constructed by comparing the desired and measured temperatures. A parametric study is conducted to demonstrate the model. (C) 2004 Elsevier Ltd. All rights reserved.