42

Yes. 42 is the answer to "life, the universe and everything" according to The Hitchhiker's Guide to the Galaxy by Douglas Adams. However, it is also the minimum temperature that fire riser rooms can be to prevent damage to sprinkler systems. By keeping the temperature at or above 42, major damage to the building can be prevented. The one thing you don't want to freeze and then thaw are fire sprinkler lines that run throughout a building. Thus, by keeping the exposed piping warm, this disaster can be eliminated.