Reply:  If the temperature is too low you might experience tarry soot in your chimney. The combustion temperature will be too low if not enough air is supplied compared to the amount of wood. Tarry soot is easily recognized as a brown sticky coat. Supply more secondary air to increase the temperature. A stove pipe thermometer placed on the lower part of the flue pipe will indicate if the air supply is correct. The flue gas temperature must be approx. 250o C. If the flue gas temperature is considerably lower, tarry soot may be created in the chimney. If the flue gas temperature exceeds 250 – 300o C, the inside parts might be superheated.