I am not a thermodynamics specialist and my brain stays where it is, but is Boltzmann not applicable here ? Heat transfer to the environment: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.html Flow between parts: https://www.efunda.com/formulae/heat_transfer/radiation/calc_2bodies_enclosure.cfm Or am i thinking too simple ? Edit: a search results in plethora of information for heat transfer by radiation or convection. http://www.auburn.edu/academic/c