A numerical study has been conducted of free convection in a tall vertical enclosure with an internal louvered metal blind. The study considers the effects of Rayleigh number, enclosure aspect ratio, and blind geometry on the convective heat transfer. The numerical model has been validated against experimental measurements and the results have been presented in terms of an empirical correlation for the average Nusselt number. The correlation is applicable to an enclosure with an internal metal blind. It has been shown that the Nusselt number correlation can be combined with a simple one-dimensional model to closely predict the enclosure U-value. (C) 2007 Elsevier Ltd. All rights reserved.