Abstract: A fuel burner assembly is provided with concentric chambers, the central chamber of which houses the fuel delivery nozzle, the annular chamber surrounding the central chamber comprising an intake and mixing chamber for receiving heated combustion air and ambient fresh air, the annular chamber being ported to pass the mixture of heated and ambient air to the central chamber to mix with the fuel delivered from the nozzle which is heated by the air mixture, the inlet ports to the annular chamber being adjustable as are the ports from the annular chamber to the central chamber, an adjustable iris baffle adjacent the upstream end of the annular chamber controls the stream of primary air delivered to the central chamber.