Duct design for an exhaust system must not only considers the demand of volume flow rate, but also takes into consideration a number of issues including system pressure balance, velocity constraint, space limitation and energy conservation. Conventional duct design methods either fail to achieve pressure equilibrium or offer poor control of flow velocity or duct diameter. A new design method that comprises two major calculation procedures: system sizing and rating is proposed. Duct system sizing problem is solved by the initial design from the conventional design methods. Feedback simulation provides the rating procedure for system actual operating process. An example is presented in this study to understand the characteristics of the proposed method. It demonstrates that the new duct design method contains a simple computation procedure and considers the pressure equilibrium under certain limits on space or flow velocity. It also provides the energy conservation strategies for the actual operating process during the design stage. (C) 2006 Elsevier B.V. All rights reserved.