In the present study, a comprehensive thermalmodeling and optimal design of a plain fin-and-tube heat exchanger is performed. Hence, the -NTUmethod is applied to estimate the heat exchanger pressure drop and effectiveness. Some design parameters of this study are selected as follows: longitudinal pitch, transversal pitch, fin pitch, number of tube pass, tube diameter, cold-stream flow length, no-flow length, and hot-stream flow length. In addition, a fast and selective nondominated sorting genetic algorithm (NSGA-II) is applied to obtain themaximum effectiveness and theminimum total annual cost (as a sum of investment and operation costs) as two objective functions. The results of optimal designs are presented in a set ofmultiple optimum solutions, called Pareto-optimal solutions. Furthermore, a sensitivity analysis of change in optimum effectiveness and total annual cost with changes in design parameters of the fin-and-tube heat exchanger is also performed in detail.