What is the natural direction of heat transfer?

Heat transfer occurs naturally from hot to cold, which is based on the principle that heat energy moves from a region of higher temperature (where the molecules have more kinetic energy) to a region of lower temperature (where the molecules have less kinetic energy). This process continues until thermal equilibrium is reached, meaning both regions have the same temperature.

Understanding this concept is fundamental in thermodynamics and HVAC principles, as it explains why, for example, a warm cup of coffee cools down when placed in a cooler room—the heat from the coffee transfers to the surrounding air. This natural direction of heat flow is a key factor in designing heating and cooling systems, as engineers must account for it to achieve desired temperature control efficiently.