Which boilers are required to have a gauge glass?

The requirement for a gauge glass is related to the need for monitoring water levels in various types of boilers. Gauge glasses are essential for providing a clear and accurate visual indication of the water level within a boiler, which is critical for safe and efficient operation.

In the context of the options presented, the correct choice specifies that all boilers are required to have a gauge glass except for steam generators and high-temperature water heaters. This is because steam generators often use alternative methods for level indication, such as electronic sensors or other technologies suited for their specific operational conditions. High-temperature water heaters, similarly, may utilize different mechanisms for monitoring water levels that are better suited for their design and operational demands.

By excluding steam generators and high-temperature water heaters from this requirement, the focus is on ensuring that other types of boilers, which may not have these advanced monitoring systems, are properly equipped to prevent dangerous conditions that can arise from low water levels. This highlights the importance of safety measures specifically tailored to the operational characteristics of different boiler types.