We examine how a thermodynamic model of the boundary of 4d-manifolds can be used for an approach to quantum gravity, to keep the number of assumptions low and the quantum degrees of freedom manageable. We start with a boundary action leading to Einstein's Equations under a restriction due to additional information from the bulk. Optionally, a modified form with torsion can be obtained. From the thermodynamic perspective, the number of possible microscopic states is evaluated for every macroscopic configuration, and this allows to compute the transition probability between quantum states. The formalism does not depend on specific microscopic properties. The smoothness and the topological space condition of the manifold structure are viewed as a preferred representation of a macroscopic space on mathematical grounds. By construction, gravity may be interpreted as thermodynamic model which is forced to be out of equilibrium depending on the restrictions imposed by matter. Instead of an ill-behaved path integral description of gravity, we obtain a non-divergent concept of sums over microstates.