Theoretical and experimental considerations of free convective heat transfer from horizontal isothermal conic in unlimited space are presented. In the theoretical part of the paper we introduced the curvilinear coordinate system compatible with conical surface and gravity field. The equations of Navier-Stokes and Fourier-Kirchhoff were simplified in this local orthogonal system. The resulting equation have been solved by asymptotic series in the vicinity of horizontal element of the cone. The final Nusselt-Rayleigh relation as a function of the conic base angle was verified experimentally. The experimental study was performed in water and air for conics with the angles equal to alpha = 0 (vertical round plate), 30degrees, 45degrees and 60degrees and diameter of the base D = 0.1 m. The experimental results are in a good accordance (maximum within +8.7%) with the theory. (C) 2003 Elsevier Ltd. All rights reserved.