The heat transfer through vertical partitions surrounded by thermally-stratified fluids is studied theoretically and experimentally. The theory is based on the Oseen linearization method. The analytical results show the effect of thermal stratification on the partition temperature, fluid flow and heat flux. The relationship between overall heat transfer (Nusselt number) and the degrees of thermal stratification on both sides of the partition is determined. The experimental part of the study confirms the heat transfer features predicted analytically. In particular, it is shown that the theoretical Nusselt number calculation is in good agreement with experimental measurements. It is shown also that the net heat transfer between the two ends of a rectangular enclosure is proportional to (1 + n)-0.61, where n is the number of vertical partitions inserted in the middle of the enclosure. © 1981.