Soot- black substance formed by combustion or separated from fuel during combustion, rising in fine particles, and adhering to the sides of the chimney or pipe conveying the smoke. My oil furnace is running, but doesn't sound as strong or clear. The notice this problem for 2 days. The smell in the basement is a strong soot smell. How can I fix this
Oil furnace with soot?

You need to tune up the burner for your furnace. This is not a good thing to do unless you have experience. Nozzle change, filter change,regap electrodes, bleed the pump, ignition transformer voltage check, and setting the draft are just a few of the items that must be done to properly tune a oil burner. The amount you spend on a burner service will be recovered by using less oil so it is a good idea to have this done.

NOTE: depending upon the amount of soot in the chamber they might have to use a soot removing powder or soot sticks to clean the combustion chamber. Soot acts like a insulation and it hinders efficiency costing you more money for oil. Ask the service man if the soot needs to be removed when he is there if he fails to mention it as part of there tune up procedures.