Lesson learned the hard way, they were not out of water completely, not even half way, but I think you guys are right about them overheating. I bought a submersible replacement so that it wont be exposed even if I do 50% water change.
They weren't completley out of the water, and amongst all of my exhaustive research, I guess I didn't read about heaters enough. If I knew better, I might not have posted the question in the first place.