(UFADS) or a stratified atria involve special thermal exchange processes that require special load calculation procedures. This paper introduces an infrared transparent (IRT) surface that enables adjacent zones to exchange thermal radiation while maintaining separate air temperatures. This paper describes the development of the IRT surface and presents a comparison of a UFADS room using the IRT model and a room with conventional air flow configuration. The fundamental principles such as infrared radiation from the zone surfaces to the cool floor, and air preheating within the under floor supply plenum are calculated with a simulation approach using EnergyPlus