Radiation

The third form of heat transfer is radiation, whereby a hot object emits infrared radiation at the speed of light. The radiation is absorbed by anything nearby that is cooler than the hot object and the absorption causes temperature to rise, without heating the air in between the hot and cold objects. You can feel heat radiation when you hold your hand near your stovetop burner or electric heater. In your house, heat radiation is often lost through the wall immediately behind a radiator if that wall is not insulated.