What type of standpipe system is commonly used in heated buildings to prevent freezing?

The wet standpipe system is the correct choice because it contains water at all times, which helps in preventing freezing. In buildings that are heated, the constant presence of water allows the system to remain functional even in colder temperatures, as the water is actively kept above freezing due to the building’s heating. This is particularly important in climates where temperatures can drop significantly, ensuring that the standpipe system remains operational for firefighting purposes.

A dry standpipe system, on the other hand, does not have water stored within the pipes; instead, it is typically filled with air or another gas until needed, making it susceptible to freezing issues. Standpipe Class II refers specifically to systems designed for use by fire departments with 1 ½ inch hoses which may not address the freezing problem directly. A manual standpipe system relies on personnel to operate and is not a specific type related to freezing prevention. Thus, the wet standpipe system is recognized as the most effective solution for mitigating freezing concerns in heated buildings.