The incorporation of an atrium into a building will not automatically lead to energy savings. The energy consumption of a parent building may be increased if compared with a similar-shaped building without an atrium. This is due to the increased need for artificial lighting, mechanical ventilation. In practice, atria are rarely incorporated in designs for the main purpose of energy saving. This research presents the relation between the passive heating and ventilating effect and the dimension of an atrium and the parent building. To achieve this purpose, an institutional single zone three story building is assumed in Tehran metrological condition. The fictitious building has an atrium and correlates with three elements of wall, glazing and air. Heat balance equation has been written for each element. By substituting the temperature profile of the atrium in the set of temperature equations, temperature of each element has been acquired. The results are in good agreement with empirical results which other researchers gathered. (C) 2011 Elsevier B.V. All rights reserved.