What is the general impact of stack temperature on boiler efficiency?

The correct choice highlights the relationship between stack temperature and boiler efficiency. As a boiler operates, fuel is combusted to produce heat, which is then transferred to water or steam. Some heat is inevitably lost through the exhaust gases that exit the boiler, which is reflected in the stack temperature.

When the stack temperature is lower, it indicates that a significant amount of heat is being retained by the water or steam, which improves the overall efficiency of the system. Conversely, a higher stack temperature suggests that more heat is being lost with the exhaust gases, thereby reducing the efficiency of the boiler. Essentially, for optimal performance, the goal is to have low stack temperatures, indicating that the system is extracting as much useful heat as possible from the combustion process before gases are vented out.

This relationship is crucial for understanding how to optimize boiler operations — minimizing stack temperature results in higher efficiency, underscoring the importance of heat recovery techniques in contemporary energy management strategies.