In the paper, the results of physical and numerical simulation of a natural convective flow formed over a heated horizontal disk with small Grashof numbers have been presented. The characteristics of the near-wall flow region and of the ascending flow one were considered in detail. On the basis of experimental and calculated data, the geometric flow characteristics, namely temperature and dynamic thicknesses, were determined. A good agreement between the experimental results and numerical simulation data was achieved. The results obtained were also compared with published data. The distribution of the vertical velocity component in the near-wall layer was determined. The analysis of the basic characteristics of heat exchange, namely the local and integral Nusselt numbers, was carried out.