The height of the fire is inversely proportional to "depth". The higher the ashing temperature the deeper the fire. The lower the ashing temperature, the more shallow the fire becomes. A deep fire means more raw coal on the top of the column. If the coal is high in volatiles, and typically the more desirable low ash coals are, it is a setup for you know what. The new controls developed after the 2011 season give extremely fine-grained control of fire depth. It's worth pointing out that a deeper fire is less likely to go out during a period of low demand. Thus, there is a bit of a balancing game that can be played here depending on user objectives. There is no perfect coal burner out there, but the Coal Gun is closer than ever. We're not going to censor or delete the thread. There is a wealth of information here, and while not everyone is kind in their remarks, we're not running away.