Which of the following is a similarity between furnaces and boilers?

Furnaces and boilers share the critical function of providing heat to buildings, but they utilize different methods to achieve this. The option highlighting high-temperature limit switches is particularly relevant because both systems incorporate safety devices designed to monitor and regulate temperature.

High-temperature limit switches serve an essential role in preventing overheating, which can lead to equipment damage or even hazardous situations. When the temperature within the system exceeds a predetermined limit, these switches activate to shut off the heating source, ensuring safe operation for both boilers, which heat water, and furnaces, which heat air.

In contrast, while piping might be involved in both systems, it differs significantly in purpose and design, especially because boilers typically have more extensive water piping systems. A low-level safety device, while important, does not apply equally to both systems. Backflow preventers are generally associated with plumbing systems rather than heating systems and would not typically be a similarity between furnaces and boilers. Thus, the high-temperature limit switches stand out as a common feature that underscores the importance of safety in both heating applications.