What condition indicates the necessity for using forced draft?

Using forced draft is indicated by insufficient natural draft through the boiler. This condition implies that the natural air circulation, which relies on the temperature difference between the inside of the stack and the outside environment, is inadequate for proper combustion. When the natural draft fails to provide sufficient airflow, it becomes essential to implement forced draft systems to ensure that the right amount of air is supplied for combustion.

Forced draft systems utilize fans or blowers to push air into the combustion chamber, effectively enhancing the combustion process. This method not only helps maintain optimal combustion conditions but also supports the overall efficiency and safety of the boiler operation.

The other scenarios, while they may pose challenges in a boiler room, do not necessarily mandate the use of forced draft. Excessive heat in the boiler room might require cooling measures but not directly compel the use of forced draft for combustion. Low combustion efficiency can be a symptom of various issues unrelated to draft mechanisms, and high pressure in the stack would likely indicate a problem with the exhaust system rather than necessitating forced draft. Thus, insufficient natural draft is the primary condition that directly justifies the use of forced draft in boiler operations.