The temperature of Heaven can be rather accurately computed. Our authority is the Bible, Isaiah 30:26, describing Heaven: Moreover, the light of the moon shall be as the light of the sun and the light of the sun shall be sevenfold as the light of seven days. Thus, Heaven receives from the moon as much radiation as the Earth does from the sun, and in addition seven times seven (forty-nine) times as much as the Earth does from the sun, or 50 times in all. The light we receive from the moon is 1/10,000 of the light we receive from the sun, so we can ignore that. The radiation falling on Heaven will heat it to the point where the heat lost by radiation is just equal to the heat received by radiation, i.e., Heaven loses 50 times as much heat as the Earth by radiation. Using the Stephan-Boltzmann fourth power law for radiation, we have (H/E)4 = 50 where E is the absolute temperature of the Earth, 300 K (27 C). This gives H, the absolute temperature of Heaven, as 798 K (525 C)! (For old-fashioned Americans, that's close to 1,000 degrees Fahrenheit. Your kitchen oven won't get nearly that hot.) (Whether the above quoted passage is intended to be a description of Heaven is open to interpretation, but it is clear from the context that it is supposed to be some sort of desirable situation.)
The exact temperature of Hell cannot be computed. However, Revelation 21:8 says: But the fearful and unbelieving... shall have their part in the lake which burneth with fire and brimstone. A lake of molten brimstone (or sulfur) means that its temperature must be at or below the boiling point, 444.6 C (above that point, it would be a vapor, not a lake). We have, then, that Heaven, at 525 C, is hotter than Hell, at less than 445 C.
The whole site is here. A very good site. Makes me laugh.