Abstract: The hot air generator according to the present invention comprises a vertical cylindrical enclosure whose walls are covered on the inside with refractory brick, the heating burner being placed at the top of the enclosure and the hot air exhaust orifice being situated at the base thereof, and in which the source of air by which it is fed is divided into three distinct flows: a first flow constituting the combustion air from the burner; a second flow constituting a first current of dilution air cylindrically surrounding the flame; a third flow constituting a second current of dilution air insufflated at the base of the enclosure so that the enclosure comprises three temperature zones: a first temperature zone which is that of the flame and is on the order of 1,800.degree.; a second temperature zone downstream of the flame and on the order of 900.degree.; a third temperature zone which is that of the second dilution current mixes with the flux of hot air which is comprised between 850.degree. and 300.degree..