Strip surface state before zinc bath immersion is linked totemperature homogeneity and gas atmosphere compositionin each furnace section. Many different gas metal reactionsoccur in the furnace that may improve the strip heatingrate or introduce surface defects, depending on theirlocalization. Gas flow models of the preheating-heating sections with hightemperature variations have been developed. They pointout temperature gradients and the competition betweennatural convection and forced convection. A model for gasexchanges between all furnace sections has been built andvalidated by gas tracing trials on industrial lines. The effect of line process parameters such as line speed,strip format and gas injection condition in all furnacessections is reported.