A new graphical tool has been developed for the HEN design of WAHEN. An H-F diagram is proposed to deal with the heat exchange matches. Nonisothermal stream mixing and splitting can be achieved by the transformation of stream composite curve in the H-F diagram. A matching composite curve is proposed for the design of HEN with parallel structure. The structure of HEN can be simplified by adjusting the shape of the matching composite curve. Both small scale and large scale examples are illustrated. Results show that the proposed method is as good as the previous methods for small scale problem, while it gets a better result for large scale problem. (c) 2015 American Institute of Chemical Engineers AIChE J, 62: 670-686, 2016