Natural convection in rectangular cavities has been studied. One of the vertical walls of the cavity is active. The opposing vertical wall is inactive and insulated from the back. The other four walls are adiabatic. Heat transfer is by convection only because surface emissivities of the walls have been reduced. Experiments are performed on rectangular cavities with aspect ratios of 1, 2.09, 3, 4, 5 and 6. All six cavities have a height of 340 mm and a depth of 210 mm. The cavity length is changed to obtain different rectangular cavities. The cavity is closed and filled with air. Thermocouples are used to measure the temperature. For each cavity, the temperature distribution between the vertical walls of the cavity is obtained at 35 positions in the length, three positions in the height and one position in the depth directions. Three regions are observed along the cavity length. In the central region, the temperature changes slightly. The isotherms are concentrated near the active wall. The variation of local Nusselt number along the cavity height is obtained. Heat transfer correlations are presented for the Rayleigh number range of 2.16 x 10(5) to 5.06 x 10(7), and for the aspect ratio range of 1-6. (C) 2016 Elsevier Ltd. All rights reserved.