  By means of the Direct Simulation Monte Carlo method, the Boltzmann equation
is numerically solved for a gas of hard spheres enclosed between two parallel
plates kept at different temperatures and subject to the action of a gravity
field normal to the plates. The profiles of pressure, density, temperature and
heat flux are seen to be quite sensitive to the value of the gravity
acceleration $g$. If the gravity field and the heat flux are parallel ($g>0$),
the magnitudes of both the temperature gradient and the heat flux are smaller
than in the opposite case ($g<0$). When considering the actual heat flux
relative to the value predicted by the Fourier law, it is seen that, if $g>0$,
the ratio increases as the reduced local field strength increases, while the
opposite happens if $g<0$. The simulation results are compared with theoretical
predictions for Maxwell molecules
