An experimental facility called the AIHMS facility has been installed and commissioned within the IIT Madras premises, to study the phenomenology of hydrogen distribution in confined spaces and generate experimental data for validation of CFD codes before further studies on hydrogen distribution and mitigation in nuclear reactor systems can be carried out. In the present article, experimental studies have been performed on the evolution of the helium stratified layer due to wall temperature induced natural convection. The base case is an isothermal release of helium within the test chamber. Subsequently, two cases are considered in which the wall temperature is above or below the gas temperature in the enclosure. Experimental data has been obtained for gas concentration at seven locations and temperatures at twenty locations within the enclosure. The results show that recirculation regions are formed near the walls. Cooler walls lead to favourable natural convection currents and promote rapid mixing of the stratified layer with lean gas mixture below. On the other hand, warmer walls lead to unfavourable natural convection currents that initially promote stratification and later on promote mixing at a slower rate. In either situation, the rate of mixing is faster than the isothermal case. Repeatability studies have been performed. (C) 2017 Elsevier B.V. All rights reserved.