  Thermodynamics plays an important role both in the foundations of physics and
in technological applications. An operational perspective adopted in recent
years is to formulate it as a quantum resource theory. At the core of this
theory is the interconversion between athermality states, i.e., states out of
thermal equilibrium. Here, we solve the question how athermality can be used to
heat and cool other quantum systems that are initially at thermal equilibrium.
We then show that the convertibility between quasi-classical resources
(resources that do not exhibit coherence between different energy eigenstates)
is fully characterized by their ability to cool and heat qubits, i.e., by two
of the most fundamental thermodynamical tasks on the simplest quantum systems.
