Heat flux through a closed window
 

Hello! I'm starting to work with FLUENT and want to simulate the flow and temperature distribution in a closed room with a radiator and a closed window. There is no air inlet or outlet, which means that energy balance can only be contained by heat flux through the thin window glass (the other real walls have a thickness of 1 m and are supposed to have a constant temperature). Is it possible to define a constant outside temperature for example as 5°C, so that the heat flux in->out (driven by the temperature difference between the room and its environment) is calculated? How can I set this in FLUENT? Thanks in advance, Stephan