5 Reasons Why Your Oil Furnace Is Producing Black Smoke

Oil furnaces are used around the world as a basic heat source, especially where temperatures drop below zero. An oil furnace tends to be quite effective but just like everything, it can sometimes run into complications like the production of black smoke. Not only is it irritating but also a harmful situation and consultation of furnace services is required. So, let’s take a look into why your oil burner might be producing black smoke and what you can do about it.

Succeeded Combustion

A lot of people are not aware of the fact that even after the furnace has been turned off, there is still some oil inside the firebox that keeps burning. Since the furnace is turned off, the fan won’t be working either and therefore, won’t be providing any oxygen to the flame that will most likely generate a thick black smoke.

The only way to solve this issue is by letting the oil burn completely before you shut it down. This means that you will need to use a calculated amount. Once the oil has been burned, you can turn off the furnace with less probability of black smoke emitting.

Dirty Furnace Components

When furnace components such as the blower fan, register grill, and supply ducts tend to accumulate dirt, dust, and smoke, the smoke from the chimney appears dark black or gray. That said, if you do not want the furnace to produce black smoke, you should make sure the components are clean.

The good news is that you can clean the components on your own as well. However, you should be careful. Furthermore, you should develop a maintenance plan, which notifies and keeps you up to date about cleaning the oil furnace.

Before cleaning the oil furnace, make sure you turn it off and use chemicals specifically designed for removing oil, tar, grease, etc. Depending on the intensity of the accumulation, you may or may not want to use slightly hard and harsh products.

Furthermore, you should also consult the user’s manual regarding the manufacturer’s recommendations for cleaning the furnace. Typically, manufacturers recommend thoroughly servicing the furnace at least once a year. Depending on your usage frequency, your furnace might need more.

Dirty Oil Filter

The oil filter is exactly what the term suggests. It is a filter designed to keep the oil away from contaminants and other impurities such as water and dirt. That said, with time the oil filter is bound to become clogged. The accumulation prevents the oil filter from functioning. As a result, the furnace begins to produce black smoke from the chimney. But, there is no need to panic.

Simply, try replacing the oil filter and see if it fixes the issue. Then again, consult the user’s manual regarding the replacement of the oil filter.

Puff Back

The components inside an oil burner have a limited time span. This means that they will start developing problems sooner or later. One of the signs is when the furnace produces a cloud of black smoke, which is a sign that the components or a certain component are not working normally. Unfortunately, you cannot troubleshoot this issue on your own and will need to call a professional. Sometimes, you will need to replace the oil furnace if it’s old.

After Fire

Another possible reason for your oil burner producing black smoke is after fire. An after fire takes place due to an oil leak or improper burning. During combustion, a small number of oil puddles on the bottom of the combustion chamber. As mentioned previously, it could also happen when you turn off the furnace and the oil continue to burn.

However, another probable cause is an oil leak. The good news here is that in some cases, you might be able to spot the leak. But if the black smoke simply does not stop, you would want to wait until the oil burns completely and then, turn off the furnace.

If that does not solve the issue, you will need to check the furnace for an oil leak. Make sure you have an expert looking for it.


An oil furnace producing black smoke can be fixed easily. If the oil furnace is new, the problem is most likely to be maintenance. However, if it’s an older unit, it might need a replacement. Regardless, you should get help from an oil burner repair service ronkonkoma on the matter.