The present work studies the Barra-Costantini passive solar heating system, with particular emphasis on the aspect of economics. The system which is studied is developed by Barra and Constantini. This system seems to be well adapted to the climatic and economic conditions in Algeria. In the first part of this work, an ideal model representing the thermal behavior of a room provided with the heating device is elaborated. The results of this model are compared with the results of an experimental study carried out on an Italian site. Initially, the model was used to deter-mine the temperature variation for the different elements of a room with the Barra-Costantini (B-C) system. The model is then used for conditions corresponding to several Algerian sites. This study makes it possible to quantify the energy savings obtained by the addition of the B-C system to a traditional gas heating system. The introduction of a ratio between the cost of energy and the cost of equipment makes it possible to conclude that only the intervention of the authorities can make the passive solar system economically viable. (C) 2003 Elsevier Ltd. All rights reserved.