  We consider dimer model on a hexagonal lattice. This model can be seen as a
"pile of cubes in the box". The energy of configuration is given by the volume
of the pile and the partition function is computed by the classical MacMahon
formula or, more formally, by the determinant of Kasteleyn matrix. We use the
expression for the partition function to derive the scaling behavior of free
energy in the limit of lattice mesh tending to zero and temperature tending to
infinity. We consider the cases of finite hexagonal domain, of infinite height
box and coordinate-dependent Boltzmann weights. We obtain asymptotic expansion
of free energy and discuss the universality and physical meaning of the
expansion coefficients.
