What factor contributes to excessive soot production in a furnace?

Excessive soot production in a furnace is primarily influenced by low airflow. When airflow is inadequate, the combustion process becomes inefficient, leading to incomplete combustion of the fuel. This incomplete combustion generates more carbon particles, which manifest as soot. An optimal airflow ensures that there is enough oxygen available for the fuel to burn completely, resulting in cleaner combustion and minimizing soot generation.

While high efficiency ratings typically indicate better combustion practices, they do not contribute to soot production. Proper maintenance is crucial in preventing soot buildup, as it ensures that the furnace operates efficiently and effectively. An undersized heat exchanger can lead to overheating, but it does not directly cause soot; rather, it may cause operational inefficiencies. In summary, low airflow significantly disrupts the balance of fuel and air necessary for efficient combustion, leading to increased soot production.