This paper shows how exergy-related variables can be used to minimize the cost of a thermal system. These variables include the exergetic efficiency, the rates of exergy destruction and exergy loss, an exergy destruction ratio, the cost rates associated with exergy destruction, capital investment and operating and maintenance, a relative cost difference of unit costs and an exergoeconomic factor. A simple cogeneration system is used as an example to demonstrate the application of an iterative exergy-aided cost minimization method.