power in = electrical heating power + radiative power in from the chamber walls
NONSENSE. The power output is not dependent on the chamber walls, therefore the power input is not dependent on the chamber walls. You're contradicting yourself, trying to have it both ways.
Radiation from the cooler walls has no effect on the heat source whatsoever. This is a basic requirement of thermodynamics!
That's ridiculous, Jane. I'm just noting that the chamber walls are hotter than 0K, so they emit radiation into a boundary around the heat source. Therefore Jane's wrong to ignore that radiation when applying the principle of conservation of energy:
What's ridiculous is your constant repetition of this bullshit idea. Yes, the cooler walls radiate inward but they have no effect whatsoever on the heat source. ALL of that radiation is reflected or scattered by the heat source. (It is not transmitted because we're dealing with diffuse gray bodies of significant mass.)
If you're being honest, then it's really too bad that you still don't understand the clear implications of the Stefan-Boltzmann radiation law. But at the same time, it makes me wonder how you got your degree.
I'm done. If all you're going to do is keep repeating these incorrect assertions, after why they are incorrect has been clearly explained to you many times, this is indeed just a waste of my time. I set out to have a scientific discussion, not to argue about your religion.