Convective: Convective heat transfer occurs when heat is transferred due to the motion of a fluid (such as a liquid or gas). There are two primary forms of convection, free convection and forced convection. Free convection occurs when the fluid naturally flows due to heat gradients. For example, hot air rises, and cold air sinks, so natural convection describes the tendency for hot air to move above cold air. As the air is in motion, some of the heat from the hot air is transferred to the cooler air. Forced convection describes situations where an external force is used to accelerate the flow of a fluid. Using a fan or stirrer to create movement in a liquid or gas would be an example of forced convection. Conductive: Conductive heat transfer is the most common method of heat transfer for solids. As heat is transferred to a solid, the microscopic atoms (or particles) that form the solid, begin to get hotter and vibrate more rapidly. The energy from the vibrations is transferred to neighboring atoms, which begin to get hotter as well. Conductive heating is typically used on solids since they have a dense, repeating molecular structure. Radiant: Radiant heat transfer is the transfer of heat using electromagnetic waves. Objects at a temperature above absolute zero emit thermal energy due to the random movement of their particles. The thermal energy is emitted in the form of electromagnetic waves, which propagate from the object. The energy in these waves can then heat surrounding objects, fluids, and gases. Common examples of radiant heat include the heat we feel from the Sun and the heat used to cook objects in a traditional oven.

In all process heating systems, energy is transferred from a heat source (such as burners and electric heaters) to a material. A material handling system transports materials through the heating system, with an enclosure often used to isolate the material from the heat source.