Architectural surfaces constantly emit radiant heat fluxes to their surroundings, a phenomenon that is wholly dependent on their geometry and material properties. Therefore, the capacity of 3D scanning techniques to capture the geometry of building surfaces should be extended to sense and capture the surfaces' thermal behavior in real time. We present an innovative sensor, SMART (Spherical-Motion Average Radiant Temperature Sensor), which captures the thermal characteristics of the built environment by coupling laser geometry scanning with infrared surface temperature detection. Its novelty lies in the combination of the two sensor technologies into an analytical device for radiant temperature mapping. With a sensor-based dynamic thermal-surface model, it is possible to achieve representation and control over one of the major factors affecting human comfort. The results for a case-study of a 3D thermal scan conducted in the recently completed Lewis Center for the Arts at Princeton University are compared with simulation results based on a detailed BIM model of the same space.