The D&D spell Endure Elements can prevent five hit points per round of damage. What temperature range does that correspond to in both directions? That is, how cold an ambient temperature does it take to cause five hit points of frost damage per round, and how hot an ambient temperature does it take to cause five hit points of fire damage per round?
The above is, naturally, true in 3.5. In 3.0, the spell's description says that it only prevents damage, and doesn't prevent "unfortunate side effects." However, we also can turn to the environmental damage rules, which say that temperatures above 90°F can inflict 1d4 subdual damage, and that those below 40°F can inflict 1d6 subdual damage on a failed save. Those could be considered "fire" and "frost" damage of a sort.