Which type of gas burner is commonly used in packaged boilers?

The correct answer is a ring burner, which is commonly used in packaged boilers due to its design and functionality. Ring burners facilitate efficient combustion by distributing gas evenly across the burner's surface, which leads to a more stable and efficient flame. This design allows for a high turndown ratio, meaning it can operate effectively across a wide range of load demands, making it highly suitable for packaged boilers that need to adjust to varying heating loads.

In contrast, other types of burners may not provide the same level of efficiency and performance required in packaged boiler applications. For instance, refractory burners are typically used in applications where high temperatures are essential, such as in industrial furnaces, and may not be as effective in the modular setting of a packaged boiler. Intermittent pilot burners are generally used in smaller, residential applications where the demand for heat is not as variable. Lastly, forced draft burners rely on a fan to push air into the combustion chamber, which is efficient but may not offer the same distribution of flame characteristics as a ring burner does in the context of packaged boilers.