Abstract: A fire prevention sprinkler system that has a warming jacket through which a warming medium, preferably water, is circulated, at a temperature sufficient to prevent freezing of those portions of the sprinkler system that contain water or another freezable liquid at times when the sprinklers are not actually spraying water to control or extinguish a fire. The warming medium is preferably heated by radiant heating, and circulation is preferably initiated by a thermostatic control whenever the temperature in the protected premises drops below a predetermined value.