Abstract: Heat-treating apparatus which includes an insulated furnace compartment through which stock to be heat-treated is passed. Perforated tubes are arranged in the furnace and they are heated to radiance by burners which also generate products of combustion which are ejected through the perforations at high velocity to impinge upon a surface or surfaces of the stock being heat-treated. The combination of radiation and convection enhanced by the impingement of the jets upon a surface of the stock provides highly efficient primary heat transfer. The burners are designed to insure that rapid combustion takes place at a point removed from the perforations to avoid flame issuing from the perforations. The tubes are sized and spaced to enhance secondary heat transfer from gases in the furnace compartment and from the walls of the compartment to the stock.