A burner for an industrial furnace has a plurality of lines passing through a furnace wall for fuel gas, burner air, and waste gas. Arranged in the furnace space is a combustion chamber (66) in which a mixture of fuel gas and burner air is combusted, and from which a flame (89) is directed into the furnace space. The combustion chamber (66) is delimited by walls (32, 65). The walls (32, 65) are arranged to be movable with respect to one another (65', 65"), so that the volume of the combustion chamber (66) is adjustable (FIG. 2).