Results are presented of 2D radiative transfer calculations performed for geometric configurations that simulate partly evacuated small-scale magnetic flux sheets embedded in the ambient solar atmosphere. Temperature distributions in (gray) radiative equilibrium at low optical depths where radiation transfer dominates the energy budget are obtained. Two-dimensional radiative equilibrium flux sheet models are calculated using a novel method which shows that the temperature enhancement of the upper layers of photospheric magnetic flux concentrations is due to the radiation channeling effect, i.e., that horizontal radiative transfer tends to channel emerging radiation into the lower opacity regions. The walls of the flux sheets are found to radiate energy from subphotospheric surrounding layers, giving rise to a strong heating of the atmosphere of the flux sheets. Radiative energy migrates horizontally from the heated flux sheets towards the ambient medium and there it heats the atmosphere at low optical depths.