Optimum design of heat exchanger networks is an important subject in process design practice. Scientists and researchers have put a lot of effort to develop new methodologies for design and optimization of such networks, using both mathematical and conceptual approaches. In conventional pinch analysis, as a conceptual approach, an initial network is first synthesized using pinch design method, and then optimized by implementation of appropriate rules and techniques. However, these rules and techniques do not involve pressure drop considerations. In a recent research, new optimization methodology has been developed that includes three stages, each of which comprises many algorithms. The first stage of this methodology, which focuses on heat load optimization, is explained in this article. The method of heat load optimization in this paper is based on this loop breaking rules and techniques, and at the same time makes use of mathematical programming to find optimum point. Due to the differences between the nature of grass-root and retrofit projects, different procedures have been developed accordingly. These new procedures have also been applied to two case studies (Aromatics as grass-root, and crude distillation unit, as retrofit) and the results proved to be as expected.Having optimized the two initial networks, 4 percent improvement in total annual cost of aromatics network and 6.5 percent improvement in investment or 11 percent improvement in payback of the CDU network were identified.