Translations:Firebox/4/en
Appearance
Having the firebox full to the brim with coal is not always the best choice. Too much coal with too little airflow negatively affects fuel efficiency , resulting in a lot of coal particles getting spewed out of the chimney before they’re fully burned. This is what makes exhaust dark. When coal amount is proportional to available airflow, however, it burns cleaner and the exhaust color is bright.