How to Calculate Internal Air Temperature in a Steel Box?

[CruiserFJ62]

I have a heat source inside a steel box. I know the outside ambient air temp and the amount of heat the source puts of. How do I calculate the internal air temp of the box?

 

[edgepflow]

Use the basic relation: Q = Delta Temperature / RT

Q = Heat Flow
Delta Temperature = Temperature (inside box) - Temperature (outside box)
Thermal Resistance = convenction and conduction resistance

Now, the inside of the box will get hot enough (increase in temperature) to get the energy of the heat source out so

Q = heat flow = heat source

Your thermal resistance will be mostly from natural convection inside and outside the box.