An innovative modelling strategy has been developed and validatedto help the design of steel reheating furnaces. A set of complementarysimulation tools has been used to rethink the furnace concept,namely the Digit@l FurnaceTM, from the burners to the global energysystem optimisation. Several Digit@l FurnacesTM are now in operationon hot rolling mills. Advantages in terms of pollutant emissions,operation costs and flexibility have been demonstrated on site.