A model for the heat treatment of randomly distributed metal parts processed in multi-zone continuous mesh-belt furnaces has been developed. The model accounts for the heat transfer by convection and radiation to the load and the belt. The effect of gas radiation due to the presence of CO2 and/or H2O gases in the furnace atmosphere has been accounted for. The effect of conduction, convection, and radiation within the parts has been considered. The effective thermal properties of the load have been calculated using a new model developed for randomly distributed parts. The effective thermal properties model has been developed using experimental data obtained from transient experiments carried out at the Thermal Processing Laboratory (TPL) of McMaster University. The continuous furnace model is capable of predicting temperature distribution within the load and the belt. It has been validated using real-life data obtained from test runs carried out at two heat treatment facilities in Ontario, Canada. The effects of load density, load emissivity and belt speed on furnace productivity have been investigated using the present continuous furnace model.