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