A furnace for performing an endothermic process, comprising tubes containing a catalyst for converting a gaseous feed, wherein tubes are positioned in rows inside the furnace, wherein burners are mounted between the tubes and between the tubes and the furnace walls parallel to the tubes rows, and wherein the burners rows and the tubes rows are ended by end walls and are divided into sections with, on each row of tubes, the distance from a wall end tube to the end wall being T2W, the distance between two adjacent inner tubes in a section being T2T, and the distance between two symmetry end tubes of two adjacent sections being T2S, wherein the tubes in the rows are arranged in such a way that the ratios T2T/T2W and T2T/T2S are greater than 0.5 and smaller than 2 thus limiting the differences in the heat transfer to the outer tubes (wall end tubes and symmetry end tubes) with respect to the inner tubes and reducing the temperature difference between outer tubes and inner tubes.