Heating elements are located on top, bottom, and both sides of chamber for enhanced temperature uniformity. Venting system is located in top of chamber to expel contaminants. High efficiency ceramic insulation surrounds chamber for maximum energy efficiency. For safety, the door switch cuts power to the heating elements when the door is opened a sensor will activate the sensor break protection and remove power to heating elements; eliminates run away conditions. Atmosphere injection is possible with pre-punched ports at rear of furnace. Optional stainless steel shelf doubles load capacity. All units include a thermocouple, models with A controllers supplied with cord and plug set, all other models require conduit connection Four temperature controller models available: Control A: basic automatic digital control holds accurately at one temperature. Single digital indicates chamber temperature Control B: Single set point automatic control allows simultaneous monitoring of the set point and actual chamber temperatures. Control C: A 2-ramp and 2-dwell programmable control.  Control D: An 8-ramp and 8-dwell programmable control that includes an RS232 port for connecting to printer or computers. Stores up to four programs