i'm designing a little project but i'm running into some environmental heat issues that i'm trying to work out. i just need a little clarification and insight from anyone willing. I have this box made of sheet steel that is going to be mounted to the side of a building. the box will theoretically be air tight so that none of the environmental elements will harm the components inside. the components inside include electronics that will do up to 70W of power and are rated to work in an environmental condition (inside the box) up to 60 C. The thing i'm trying to figure out is what temperature it would have to be outside of the box (i'm first trying to do this without considering direct sunlight because that's really difficult to do) where it would put the box temperature over 60 C and destroy the components. this is what i'm thinking. after some reasonable amount of time of letting the electronics run, some sort of equilibrium will occur between the temperatures inside and outside the box. at that point the rate of heat transfer due to conduction through the sheet metal will be equal to the rate of heat production by the electronics (70W). so using fourier's law (the rate of heat conduction): dQ/dt = k*A*(T_in - T_out) / x where: dQ/dt = rate of conduction k = steel's conductivity constant A = surface area exposed to environment T_in = temp inside box T_out = temp outside box x = thickness of sheet metal we can conclude that the temperature inside the box will only be slightly hotter than the temp outside. So if what i did was true then the temperature would have to reach a really high 58 C or so to compromise the electronics functioning capacity?