There are 3 important mechanisms of heat transfer: conduction, convection, and radiation. In all of these mechanisms, the rate of heat flow between an object and its surroundings increases with the temperature difference between object and surroundings. Supply energy to an object at a fixed rate, and its temperature will rise until the heat flow to its surroundings is equal to the rate at which energy is supplied. The object is then in thermal energy balance, and its temperature remains constant.