The aim of the present work is to include an uncertainty into classic thermoeconomic analysis in order to find solutions that simultaneously satisfy thermodynamic and economic goals. Thermoeconomic optimisation has been considered as a fuzzy nonlinear programming problem where local criteria: maximum energy (exergy) efficiency and minimum total cost rate as well as different constraints in an ill-structured situation can be represented by fuzzy sets. The trade-off or the Pareto domain, where the value of the thermodynamic criterion cannot be improved without the value of the economic criterion being worsened, has been considered as a first step of the optimisation strategy. The Bellman-Zadeh model as the intersection of all fuzzy criteria and constraints has been used for final decision making. Case studies of fuzzy thermoeconomic analysis application have been presented.