  Advanced 3D radiative MHD simulations now reproduce many properties of the
outer solar atmosphere. When including a domain from the convection zone into
the corona, a hot chromosphere and corona are self-consistently maintained.
Here we study two realistic models, with different simulated area, magnetic
field strength and topology, and numerical resolution. These are compared in
order to characterize the heating in the 3D-MHD simulations which
self-consistently maintains the structure of the atmosphere. We analyze the
heating at both large and small scales and find that heating is episodic and
highly structured in space, but occurs along loop shaped structures, and moves
along with the magnetic field. On large scales we find that the heating per
particle is maximal near the transition region and that widely distributed
opposite-polarity field in the photosphere leads to a greater heating scale
height in the corona. On smaller scales, heating is concentrated in current
sheets, the thicknesses of which are set by the numerical resolution. Some
current sheets fragment in time, this process occurring more readily in the
higher-resolution model leading to spatially highly intermittent heating. The
large scale heating structures are found to fade in less than about five
minutes, while the smaller, local, heating shows time scales of the order of 2
minutes in one model and 1 minutes in the other, higher-resolution, model.
