heating system indicated in the drawings and as described herein the venturi section 31 and the fuel jet nozzle 33 provide aspiration by drawing hot waste gases from the waste heat fuel 16 through the conduit 45 reversing valve 47 insulated conduit 53 and spool piece 55 into the venturi section 31 so as to flow around the fuel gas jet nozzle 33 the waste gas is prevented from flowing into conduit 51 because the waste heat reversing valve 47 is so positioned that the waste heat gases can flow only into conduit 53 the waste heat gases mix with the rich fuel gas in the lower portion of the venturi section and provide the desired dilution of the fuel gas then the mixture of fuel gas and the hot air from the regenerative system flow into the gas gun 29 and thence into the gun flue 25 the diluted gas mixture burns in the heating flues with the desired 34 long flame 34 the products of combustion are withdrawn from the 34 on 34 flues into the downdraft or 34 off 34 flues 65 67 and then to a regenerator and into the waste heat flue 16 as for the flues in the 34 off 34 heating walls the waste heat reversing valves 47 and the fuel gas reversing valves 37 are in the off position and the waste heat shutoff valves 49 are open the carbon caps 57 as mentioned previously would be opened after a slight delay by the reversing machine when the respective heating walls 65 67 are off then decarbonizing ambient air flows through the venturi 31 and the gun flue 25 to the risers 27 and thence through the fuel gas nozzles not shown and the.