What are the pressure and temperature limits for steam heating boilers?

The correct answer reflects the widely accepted standards for the operation of steam heating boilers. A steam heating boiler is typically defined as a boiler that operates at pressure not exceeding 103 kPa (15 psi) and a temperature not exceeding 121˚C. These limits are significant because they delineate the classification of low-pressure boilers, which are subject to less stringent regulatory requirements compared to higher-pressure systems.

Low-pressure steam heating systems are commonly used for space heating and can be found in various applications such as residential heating, large buildings, and industrial processes where high pressure isn't necessary. By operating within these limits, the boilers ensure both safety and efficiency, minimizing the risk of hazardous conditions associated with high-pressure steam.

The other options present values that exceed or do not align with the typical definitions and classifications for steam heating boilers, making them inconsistent with standard industry practices. Thus, option B accurately specifies the limitations within which such boilers function safely and effectively, making it the correct choice.