This paper focuses on presenting a technique to calculate energy retrofit horizons in process plants. In particular, it focuses on crude fractionation units. The methodology takes advantage of two facts: (a) Pinch-type calculations can be performed using operator type representations and (b) Processes like crude fractionation offer large flexibility in the operating/design parameters. This paper builds on the well-known sequential technique of performing pinch analysis after fixing operating conditions, particularly including heating and cooling targets. The paper analyzes the mathematical properties of the newly introduced implicit pinch operator.