Vertical enclosures with conducting fins attached to the cold wall were considered. Side walls were kept at constant but different temperatures, while horizontal top and bottom walls were insulated. A conjugate formulation was used for the mathematical formulation of the problem, and a computer program based on the control volume approach and the SIMPLE algorithm was developed. Computations were performed to investigate the effects of the fin configuration and Rayleigh number on the flow structure and heat transfer. It was observed that the heat transfer rate through an enclosure can be controlled by attaching fins to the wall(s) of the enclosure. At low Rayleigh numbers (conduction controlled regime), the heat transfer rate increases with the increasing number of fins and the fin length. However, at higher Rayleigh numbers (convection dominant regimes), the heat transfer rate can be decreased or increased by properly choosing the number of fins and the fin lengths.