Abstract This contribution presents an alternative approach to thermal physics and to its affiliated thermodynamics aiming to initiate a discussion concerning the related problems of its fundamental nature. We reason that the classical thermodynamics suffers considerably from a misinterpretation of experimental facts known as the Principle of Equivalence of Energy and Heat and from the resulting introduction of a troublesome quantity called entropy lacking clear physical meaning within the traditional thermodynamics. As this concept generates an endless chain of paradoxes connected mainly with the Second Law of Thermodynamics , we propose to change the structure and the conceptual basis of thermal physics prior to the solving of more complex problems involving, e.g., the application of quantum or stochastic electrodynamics to the relativistic thermal phenomena. We argue that a good candidate for such a more satisfactory theory is modified Carnot's theory reintroducing an old–new physical quantity historically named caloric. An introducing outline customizing the reader with the basic ideas of this alternative version of the classical thermodynamics is thus given. Principal relations of the caloric theory are presented, together with illustrative treatment of some common tasks of the thermal physics. Use of the caloric theory to description of real heat engines is also presented.