This paper presents the results of a parametric study of a prototypical single-family ranchstyle house. The DOE-2.1B energy analysis simulation program was used to analyze the variation in heating, cooling, and total energy requirements and resultant energy costs due to changes in the following building characteristics: fenestration orientation, size, conductance, and shading coefficient; and levels of internal heat. gain, infiltration, and natural ventilation. Climatic sensitivity was established by considering results from Madison, Wisconsin, and Lake Charles, Louisiana. To facilitate simplification of the analysis, multiple regression techniques were used to generate a simplified algebraic expression that relates energy use to the parameters varied. This simplified representation of the performance data could form the technical basis for simplified design tools to define optimal fenestration configuration parameters.