are located above the level of air outlets 20 and fuel gas outlets 32 in that the internal burner 14 is lengthened this leads to a long annulus or annular space 34 in the combustion zone which is favourable for a uniform mixing and combustion action as well as for a uniform heat transfer optimum effects can be obtained with the shaft furnace according to the invention if as is all the represented embodiments the different lateral outlets for the combustion pipes fuel gas outlets and air outlets are provided in the different arrangements both in the furnace shell 10 and in internal burner 14 in all the embodiments the fuel gas can be supplied to the lateral fuel gas supply lines 36 on the one hand and the fuel gas supply line 28 of internal burner 14 on the other from a third bustle pipe 56 surrounding the furnace shell fig5 shows an embodiment of the shaft furnace according to the invention in which combustion chambers 58 with combustion tubes 60 mounted thereon are provided the use of such combustion chambers 58 with or without mounted combustion tubes 60 makes it possible to use non gaseous fuels in the case of gaseous fuels firing can take place by means of the fuel gas supply line 28 of internal burner 14 and or fuel gas supply line 36 on the outside of furnace shell 10 in the.