I'm taking your question to be tongue in cheek. However, if you are serious, perhaps you could explain what you mean by the terms exothermic and endothermic in terms of "Hell." I have an initial take on the question but perhaps, if you are serious, you could enlighten me as to your real meaning.
First of all, the Bible "Hell" is the grave not some fiery pagan torture chamber. In the real hell there's not a lot of thermal activity going on unless of course one is buried in a seismically active plot of ground. However in terms of one's real experience, even then the question is irrelevant. The dead are unconscious. Kaput. The only hope of salvation is in the resurrection. (See 1 Corinthians 15:17-19)
If I had to choose, I would say that the process of death and corruption in "Hell" is exothermic. That is to say, any heat produced by the decaying body is transferred to the environment. Here are a couple of links to information on this subject in the website. Click on the titles to access: