Energy System Retrofit is an important activity for simultaneously improving resource efficiency, economic performance and contribution of industry to sustainability. While identifying thermodynamically and technically feasible options for retrofit-based energy savings is an important necessary step, it is not a sufficient one for achieving real savings. A further necessary step is the selection of a set of economically feasible and attractive ways of implementing the identified retrofit options. This paper provides an analysis of the investment planning concepts as applied to the retrofit of Heat Exchanger Networks (HENs) and identifies the key issues for retrofit implementation and planning. The paper concludes with the formulation of further research goals, aimed at the establishment of an integrated method for optimal planning of retrofit investments in energy systems.