For which of the following devices is the setting of 140° F typically used as a low temperature limit?

The low temperature limit setting of 140° F is typically associated with boilers, particularly those that operate on hydronic heating systems. This temperature limit is crucial for preventing issues such as condensation in flue gases that can lead to corrosion and inefficiency in the system. Maintaining a minimum temperature helps ensure that the boiler operates efficiently, provides adequate heating, and prevents the potential repercussions of low return water temperatures, which may not fully utilize the heat exchanger's performance.

In contrast, pressure-reducing valves do not operate based on temperature settings, but rather on the pressure of the fluid. Zone valves, which control the flow of hot water or steam to individual areas in a heating system, focus more on operational convenience rather than a fixed temperature limit. Pumps are typically designed to transport fluids and are not limited by temperature settings either.