Heat transfer. Illustration showing three forms of heat transfer. Radiant heat is thermal radiation emitted by matter, and can be felt from the sun across the vacuum of space. Radiant heat from a fire heats surrounding air which expands and rises, transferring heat upwards by convection; this can be felt above the fire. Conduction is the transfer of thermal energy between particles in a material: the cool end of a metal rod will become hot if the other end is placed in a candle flame, as heat is conducted down the rod.