In this first part of a two part problem, a process model for control of a batch type heat treatment furnace with low NOx radiant tube burner has been developed. The model considers coupling between the different components and the wide variation in time scales of the processes involved. The heat transport between the gas stream and the radiant tube is modeled by a conjugate convection-radiation mode using an empirical correlation for the convection and an optically thin radiation model. The combustion is considered in a highly pre-heated and diluted mode with single step modeling of the chemical kinetics. The heat transfer between the radiant tube and the load is considered to be only through radiation. The model is used in the companion paper to generate optimal operating conditions for the desired performance and emission characteristics. (c) 2004 Elsevier Ltd. All rights reserved.