The mixing of combustion air with flue gases is an effective method for reducing NOx emissions, and the entrainment of furnace gases into the jet emerging from a burner can provide the correct proportions of internal mixing. This paper presents a diffusion-type burner that gives extremely low emission of NOx through intensive entrainment of the furnace gases into the jet before the flame reaches its maximum temperature. The main objective here is to provide experimental evidence that NOx formation can be reduced when the gas dynamics of entrainment lead to a reduction of flame temperature in industrial-scale high-temperature furnaces. It has been demonstrated that for burner loads of 290 kW and 660 kW it is possible to obtain NOx emissions below 30 ppm during combustion of natural gas in a furnace with an inner-wall temperature as high as 1200 degrees C.