What Causes Black Smoke From an Oil Furnace?

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Smoke of any color -- white, gray and black -- coming from your oil furnace chimney frequently indicates a problem with your oil furnace. Contact a heater repair technician to inspect your oil furnace, diagnose the issue and make the necessary repair. Although the problem may be as minor as a filthy system component, black smoke may point to a more serious problem that requires replacing failing system parts to avoid a possible safety hazard.

Dirty Components

When components, such as the register grill, supply ducts and blower fan compartments, build up with dust and dirt, smoke released from the chimney appears dark gray or black. These components must be dirt and dust-free in order for the oil furnace to operate efficiently. Clean these components with a vacuum cleaner and soft, dry rag at least once a year. Refer to the manual for instructions relevant to your furnace. A dirty oil filter is another component that can become clogged with impurities and need cleaning. The oil filter works to clean the oil supplied to the furnace. When the filter is blocked, it cannot effectively remove dirt and water from the oil, and thus the oil furnace burns dirty oil that results in black smoke discharging from the chimney. Contact a repair technician to clean and possibly replace the oil filter.

Puff Back

Oil furnaces and their components have limited life spans. When your oil furnace malfunctions it can cause a puff back or delayed ignition that happens when atomized oil travels to the combustion chamber, but does not ignite right away. Once the pilot eventually ignites, an eruption in the firebox occurs that is generally marked by a bang accompanied by a cloud of black smoke. Depending on the force of the explosion, smoke either fills the room of the furnace or dispenses out the chimney. When this problem takes place, contact the fire department as a precautionary measure and vacate the premises until the smoke clears out. The smoke contains toxins that are harmful to ingest. Phone your heater repair technician who can thoroughly inspect the oil furnace for damage and perform repairs.

After Fire

Even after the burner cycles off, accumulated oil in the firebox burns and causes an after fire. Once the burner is off, the fan also stops running and oxygen is no longer delivered to the flame. An oxygen-deprived flame generates thick, black smoke that exits the chimney. Smoke continues to billow as long as the fire burns and until the fire is either put out or the oil is used up. Although the problem normally poses no immediate danger, since the firebox is designed to withstand intense heat of a fire, you should contact a heater repair technician to examine your oil furnace and fix it.


Christie Gross

Christie Gross has been writing since 1998. Her work writing public policy platforms for elected officials nationwide has been featured in national and local newspapers under various client pen names. Gross has a Bachelor of Arts in English and political science, as well as a Master of Public Administration from the University of Delaware.