What does the difference in the two fires in the office reveal about the kind of boss Scrooge is?

Miser and ungenerous person.

Explanation:

In the office, there were two fires. One in Scrooge's office and the other in his clerk's office. Scrooge's fire was a small fire but the clerk’s fire was even much smaller that it looked like one coal.

The difference in the two fires inside the office reveal that Scrooge was a miser and ungenerous person.

Though both the fires were already too small, his clerk's fire was way much smaller that he would often warm himself at the candle. Scrooge did not even bother to consider his clerk's situation.