Just how hot does it need to be in order to be "hotter than hell"?
First, let's try to figure out just where Hell is located. Most religions describe Hell as existing deep underground. Presumably, Hell is the same distance from New York as it is from Beijing as it is from London, so, for argument's sake, let's stick it at the center of the Earth, in the planet's super-hot, iron core.
Now, scientists have yet to directly measure the temperature of the Earth's inner core, but most estimates put it at somewhere between 9,000 and 11,000 degrees Fahrenheit. That's pretty hot. Hot enough, in fact, to melt that iron-alloy ball under normal conditions, but the constant weight of the rest of the planet pressing down on it keeps the core, which is about one third the size of the moon, solid. (Hot enough to melt iron, but apparently not quite hot enough to melt one's eternally-damned soul.) [Read: How Much Does a Soul Weigh? ]
You might be wondering, "why is the center of the Earth so hot?" Well, it's the combination of two things. First, all the radioactive materials in the Earth generate heat. Second, there's the leftover heat from the formation of the planet. When all the matter that created Earth came together, it picked up kinetic energy as it did so. When it came to rest in a proto-Earth ball, that energy had to be conserved, and so it transformed into heat, which is still being slowly emitted.