The novelty of this paper is the coupling between a thermosiphon collector and a single zone with the following details; a thermosiphon system (TYPE 45) which uses the solar energy as an unlimited renewable energy to produce the heat by using an internal coupling of a flat plate collector and a storage tank in a closed loop realized in TRNSYS. Consequently, the user simply utilizes TYPE 45 as thermosiphon ready to be run, and a single zone (TYPE 19) is a complex type which is designed for residential buildings that can be specified by the user in order to obtain an acceptable heating within a house. The user specified the characteristics of the internal space, external weather conditions, walls, windows, and doors. To facilitate this description, the parameters and inputs for this component are organized in separate table according to a logical structure. According to us, the choice of this model of thermosiphon coupled with a single zone can have multiple interesting engineering applications, in particular ameliorating the mode of the heating in residential buildings. Two flat plate collectors of aperture area of 6 and 8 m(2) are modeled. The solar fraction of the entire system is used as the optimization parameter. The temperature of the water in the storage tank, the collector's temperature, the temperature inside and outside the house, the solar fraction for different collector areas and the total energy were also measured in 11 h operation in January and 2880 h operation in winter. The average solar fraction obtained was 85% and the system could cover all the hot water needs of a house of six people. The maximum auxiliary energy was needed during 11 h operation in January and 4 months in winter. The results show that by utilizing solar energy, the designed system could provide 40-70% of the hot water demands in winter. (C) 2013 Elsevier Ltd. All rights reserved.