For reducing the life cycle cost of the facilities, it is important to select the proper treatment based on the facility condition at the time of decision making such as the time of preventive maintenance. For example, we need to decide whether we should replace a lower level item or an upper level item in the case of a lower level item failure of the facilities with a hierarchical structure. In this study, we propose a method to estimate the expected extent of deterioration and failure effects which would occur in the future, based on the operation and maintenance history as well as the current operating conditions, and to determine the appropriate treatments. In this method, we take the complementary functional relationships among facility components in the case of redundant structure into consideration in evaluating the failure effects. The method has been applied to the multi-sprit type air-conditioning system of a commercial building to illustrate its effectiveness.