Is Hell exothermic (give off heat) or endothermic (absorbs heat)?
If you want to be objective about it, I recommend you start with Boyle’s Law Boyle's law - Wikipedia (gas cools when it expands and heats when it is compressed), or some variant.
“Some” people however, have different ideas 
First, we need to know how the mass of Hell is changing in time. So we need to know the rate at which souls are moving into Hell and at the rate at which they are leaving. I think that we can safely assume that once a soul gets to Hell, it will not leave. Therefore, no souls are leaving.
As for how many souls are entering Hell, let’s look at the different Religions that exist in the world today. Most of these religions state that if you are not a member of their religion, you will go to Hell.
Since there is more than one of these religions and since people do not belong to more that one religion, we can project that all souls go to Hell.
With the birth and death rates as they are, we can expect the number of souls in Hell to increase exponentially. Now, we look at the rate of change of the volume in Hell because Boyle’s law state that in order for the temperature and pressure in Hell to stay the same, the volume of Hell has to expand proportionately as souls are added.
This gives two possibilities:
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If Hell is expanding at a slower rate than the rate at which souls enter Hell, then the temperature and pressure in Hell will increase until all Hell breaks loose.
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If Hell is expanding as a rate faster than the increase of souls in Hell, then the temperature and pressure will drop until Hell freezes over.
So which is it?
If we accept the postulate given to me by Sarah F. during the third year of my undergraduate days (I did Telecoms), “it will be a cold day in Hell before I sleep with you”, and take into account the fact that I slept with her a fortnight after she said this, then number 2 must be true, and thus I am sure that Hell is exothermic and has already frozen over.
The corollary of this theory is that since Hell has frozen over, it follows that it is not accepting any more souls and is therefore extinct… leaving only Heaven thereby proving the existence of a divine being which explains why that very night, Sarah F. kept shouting “Oh my god!”
