Building energy consumption has increased in China with the rapid urban development and population growth of recent years. Based on the hot climate in Chongqing, two types of experimental chambers were constructed to investigate the effects of external wall insulation on energy consumption and the indoor thermal environment. An 'energy efficient' chamber was constructed using a thermal insulation system for the external wall, and a 'basic' chamber was constructed according to the general design for residential buildings of the 1980s and 1990s. Analysis of the experimental data for power consumption and the thermal environment of the two chambers showed that the indoor thermal environment of the energy efficient chamber was less affected by the outdoor environment and could be maintained at more comfortable conditions with less energy consumption than the basic chamber. The energy consumption of the energy efficient chamber was lower than that of the basic chamber, offering a savings of up to 23.5% in air conditioning energy consumption during the summer-time test period. Therefore, the results of this study demonstrate that use of an external wall insulation system can improve building energy efficiency. (C) 2014 Elsevier B.V. All rights reserved.