Current methods of evaluating the risk of condensation on fenestration systems generally include two-dimensional computer modeling and sometimes laboratory testing. This is not sufficient for curtain wall systems that incorporate areas of insulated spandrel. In most curtain walls, mullions can extend from a warmer interior environment into a colder insulated spandrel. The mullions function as thermal bridges and may increase the potential for condensation on or within the system. The impact will vary depending on several factors such as the type of vision and spandrel glazing, insulating glass unit (IGU) spacer type, insulation thickness, location of the insulation, and vapor barrier methodology. Industry standard evaluation methods do not address this heat transfer. Two-dimensional computer modeling can be used to assess transitions between vision and spandrel areas. Because it is only a two-dimensional evaluation, it cannot determine the heat flow in the third dimension. Laboratory testing such as the American Architectural Manufacturers Association’s AAMA 1503, Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors, and Glazed Wall Sections, is sometimes used to provide measured results of condensation resistance. Manufacturers typically do not include spandrel conditions when testing the performance of a system. The purpose of this paper is to evaluate the relative impact of three-dimensional heat flow through curtain wall vision/spandrel conditions related to the potential for condensation to determine if there is an increased risk of condensation at the vision/spandrel interface and to demonstrate that the use of three-dimensional thermal modeling can be readily repeated for multiple project specific variables without the cost of laboratory testing.