Abstract: A convection furnace for a tempered glass sheet (1), into which furnace the glass sheet arrives along a hauling track, as on turning rolls (3), and the furnace has also heating resistances (5) against glass sheet (1) for heating the blast air, a blast apparatus and blast channelling (4), (2) for blasting said air against the glass sheet. The blast channelling comprises elongated channels (2) in the glass sheet (1) direction, inside of which there is at least a part of each blast air heating resistance (5) and each channel (2) has below the resistance line a broadening and in the broadening a bottom part (9), whereby bottom part (9) is furnished with blast holes (7, 8).