The present study was undertaken in order to gain understanding of certain aspects of natural convection in a glass-melting tank heated locally from below. Based on numerical predictions, the effects of Rayleigh number, geometry of heated strip and tank on the flow patterns and heat transfer are investigated for Rayleigh numbers in the range 10(2) to 10(7), strip width to tank length ratios 0.1-0.5 and half-tank aspect ratios 1.0, 3.0 and 7.0. The effect of the heated strip position is studied by placing it at centre and off-centre positions at the tank bottom wall. The effect of Rayleigh number on heat transfer is found to be significant. The Nusselt number is obtained as a function of Rayleigh number, heated strip width to tank length ratio and tank aspect ratio. Augmentation of flow circulation intensity and fluid temperature results when increasing the tank length and strip width. A scale analysis led to a behaviour which is confirmed by the numerical results. (C) 2004 Elsevier Ltd. All rights reserved.