Dry pipe systems are the second most common sprinkler system type. Dry pipe systems are installed in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable. Dry pipe systems are most often used in unheated buildings, in parking garages, in outside canopies attached to heated buildings (in which a wet pipe system would be provided), or in refrigerated coolers. In regions using NFPA regulations, wet pipe systems cannot be installed unless the range of ambient temperatures remains above .