Heat treatment is typically carried out in furnaces; the furnaces can be heated using fuel or by electrical resistance. Typically, heating equipments which operate at lower temperatures are called ovens; however, in this module, we call all devices used for heating materials as furnaces.

The heating in a furnace takes place either through conduction or convection or radiation or any combination of these. Generally, higher temperatures involve heating through the mechanism of radiation.

The heat transfer media in a furnace can be gaseous or liquid; there are also furnaces with fluidised bed as the heat transfer media. In some cases, the furnace might be evacuated (vacuum furnaces); it is also possible to introduce controlled gaseous atmospheres (for example, Argon, steam, dry hydrgoen, and so on) in the furnace.

The heat treatment can be carried out in two ways: either batchwise or continuously.

It is common for workpieces that are to be heat treated to be kept in fixtures, baskets and trays to avoid distortion during heat treatment.

Of course, the most important aspect of furnace operation is the control on temperature. Temperature sensors and thermocouples along with temperature controls are, probably, the most important parts of a furnace.