How does heat affect the orbit?
You vaporize one side of the object, and the expanding gases provide some thrust.
I'm not sure you'd even need to vaporize anything. Ever seen one of these?
I assume you're implying radiation pressure could push things out of orbit. Perhaps, but that device doesn't demonstrate radiation pressure.
The Crookes Radiometer depends on air molecules being present to work. It spins with the dark side of the veins trailing, in the opposite direction you would expect from light pressure (for which the light side has a greater impulse due to recoil of the photons instead of absorption.)
In theory, radiation pressure could indeed push objects out of orbit, but I'm too busy/lazy right now to run the numbers to find out how much energy it would require. Also, consider Newton's third law: any decent impulse given to space junk by the ISS using radiation pressure would affect the ISS as well.