TDA Research, Inc (TDA) is developing a compact lightweight emergency system that provides 30–minute life–support in the case of system or component failure in the Portable Life Support System (PLSS). This emergency system is based on a regenerable sorbent technology developed at TDA, which removes carbon dioxide (CO2) and moisture (H2O). The emergency Extravehicular Activity (EVA) system must control CO2 levels as well as humidity and temperature. Two thermal sources that must be managed are the metabolic heat from the astronaut, mostly in the form of water vapor and the heat released from the exothermic reaction of CO2 and H2O with the sorbent. Consideration of the thermal management is critical in the design of this system because it affects sorbent performance. Additionally, it is important in maintaining astronaut comfort. In designing the low venting EVA emergency system we determined how to manage these thermal loads in a lightweight design while maximizing sorbent effectiveness. A Sinda/Fluint model for radiation was developed to optimize the design of components. This paper discusses the thermal management important in maintaining the CO2, H2O and temperature control.