What Causes Soot Build Up in Oil Furnaces?

Soot Buildup

• Soot builds up over time inside your furnace, flue and chimney, and can be removed by regular maintenance. If you look inside your furnace's damper door -- carefully, as it may be hot -- you can judge the amount of soot buildup and decide if cleaning is necessary. An annual cleaning should be enough to keep soot from becoming an issue. If your furnace constantly has soot buildup, even with regular maintenance, any of a number of problems could be to blame.

Soot Buildup Causes

• Excessive soot production in an oil furnace can indicate a problem with the burner, which burner can be dirty, clogged, or simply old and in need of replacement. Your furnace may also be in need of an air adjustment. If the burner simply needs to be cleaned, you can probably take care of it yourself, but a more serious problem will require expert assistance. In some cases, excessive soot could indicate an underlying installation problem, such as a too-short chimney that allows inadequate draft, leading to sooty burner operation.

Puffbacks

• A separate soot problem, called a puffback, occurs when unburned or partially burned oil leaks back into the combustion chamber at the end of a heating cycle. The oil then explodes when the furnace ignites again, causing a "puff" of soot to be blown out of your furnace into the room. Puffbacks can damage various parts of your furnace depending on their severity, and if they are occurring you should call a furnace technician as soon as possible.

Puffback Causes

• Puffbacks can have several causes, but they are all related to oil somehow making its way back into the chamber after a cycle. A leak in the oil supply piping may be to blame; a leak allows air into the pipes, which pushes unburned oil out of the spray nozzle and back into the ignition chamber. In other cases, oil burner shutdown problems cause oil to leak out after it has stopped burning. Poor oil burner maintenance can also cause puffbacks, often due to a dirty spray nozzle.