Heat transfer is an essential thing in every environment from nano scale to macro scale. Everywhere around us, inside us, on cell level, atomic level, organ level to body level. All the biological processes are connected to heat release on one hand and to heat absorption on the other hand, whenever two entities with different temperatures interacts directly or indirectly through some media physically connected to both entities. The most common heating medium is air. Number two belongs to water. Thanks to warming air we can feel the warmth of fireplace. When using a steel stick we can intensify the feeling of fireplace warmth rapidly. In the first case we talk about radiant heat transfer ¿ through air. Second, more intensive is called conduction. There is another way of heat transfer called convection. Convection is connected to natural heat flux. The heat flows up as the warmer air always rise up above colder layers of the air or other liquid medium. The Law of conservation of Energy applies to heat transfer. The law of conservation of energy states that energy may neither be created nor destroyed.