The Heat Recovery Steam Generator is an integral and critical component of the Combined Cycle Power Plant. In the conceptual stage of the project it is very difficult to select the steam conditions for the optimized plant configuration. At this point most of the parameters are not well defined and since they are interdependent on each other, it is hard to optimize. The paper presents discussion of what parameters are influenced by the type of circulation and how the selection should be made. The user can evaluate the critical parameters and select the circulation most advantageous for that particular plant.