Furnaces are built of several kinds of high temperature hot zone  materials to heat the  process material and insulation (refractory, ceramic or graphite ) without breaking down during the several months and years of service.

Specifications to consider when searching for vacuum furnaces include process temperature, height, width and length [or diameter and length]  of the desired work space,  vacuum or partial  pressure range, cooling rate. 

The process temperature is the maximum temperature at which the unit may operate and still maintain rated performances.

The height refers to the internal height dimension of the unit. The width refers to the internal width dimension of the unit, or for vertical top load, bottom load, or bell jar style furnaces, the outer diameter of the desired hot zone work space. The length refers to the length dimension of the hot zone work space..

The vacuum or pressure range can be “Rough” to “ Ultra high vacuum”, rough vacuum  (1 Torr), medium (10^-3 Torr), high vacuum (less than  10^-3 to 10^-8 Torr), ultra-high vacuum ( less than  10^-8 Torr), and elevated pressures (greater than  760 Torr).

Common configurations for vacuum furnaces include front loading box, bottom loading elevator, front loading horizontal, split clams shell, top loading vertical, tube, batch, semi-continuous or , continuous.   These refer to the shape of the vacuum vessel, and how they are loaded and unloaded.

Vacuum furnaces typically are used for the absence of air, or in inert or reducing environments.  Special provisions must be made at high temperatures and oxidizing environments such as using ceramic hot zone heating elements and insulation.

Furnaces may have either a single set point or a programmable controller to adjust temperature and temperature stability.  Other features include over temperature protection, three-zone or multi-zone, computer interface, application software, view ports, and service or entry holes

Choices for heat source include: arc, electrical  low secondary voltage AC [or DC] resistance, induction, infrared, plasma  RF, or microwave.