Abstract: Apparatus for monitoring product temperature in a furnace, the furnace being of the open ended and secondary emission type, and having a plurality of serially arranged heating zones therein, each of the zones being adjustably heated. The furnace includes a conveyor which passes therethrough for carrying product thereon through the furnace. As is conventional, the furnace includes an outer casing or wall and an inner muffle with a cavity therebetween. Heaters are provided for applying heat to the cavity to heat the wall of the muffle. Tubes are provided for passing through the casing and into the muffle so that temperature sensing means may pass through the tubes into the muffle superimposed of the conveyor. The temperature sensors are connected to a monitoring system for amplification and for monitoring the temperatures directly of at least the critical zones of the furnace so that adjustment of the temperature may be made within preselected zones without causing loss of product.