A 9.5 mm-diameter, horizontal, cylindrical heater was traversed horizontally and vertically within a 750 mm long, 350 mm x 350 mm square-sectioned relatively-cold enclosure for two values of the Rayleigh number, namely 7.0 x 10(4) and 1.0 x 10(5). The maximum steady-state rate of natural convection occurred when the heater was located parallel to and near a vertical wall (i.e. with 0.25 < Y< 0.5, S-h/d = 1.5).