Abstract: A door assembly for use with a furnace having a furnace wall and a door opening through the furnace wall. The door assembly includes a ceramic body with at least one aperture therethrough and a metal door facing secured to the ceramic body, the metal door facing having an aperture in register with the bore in the body. At least one of a peep hole assembly or a probe assembly is connected to the door assembly such that the interior of the furnace can be viewed through the peep hole assembly or the probe can be exposed to internal conditions in the furnace.