• conduction
• convection and
• radiation

Conduction: HT process where the energy is transferred between molecules of matter actually contacting one another. As the temperature of the molecules increase, so they vibrate faster and thereby contact more frequently.

Convection: HT process where the energy is transferred by the flow of molecules actually transporting the energy with them by virtue of their temperature.

Radiation: HT process where the energy is transferred without any need for molecules of matter, the flow of energy is by electromagnetic radiation (emr), in exactly the same way as light travels from the sun to earth.