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What Every Furnace Owner Needs To Know About Smoke And Soot

by Ricardo Hart

If you recently noticed smoke coming out of your air vents, you likely got worried about whether or not a fire was in progress or about to start. Activating a furnace is the common culprit for this type of occurrence, but whether or not it is dangerous is dependent upon a few things. The following information will give you a better understanding of the potential dangers these conditions pose and why you need to use an HVAC professional as a resource to determine why your furnace is smoking.

Risks of Smoke and Soot

Carbon Monoxide Risk

Gas furnaces may release carbon monoxide, which can result in sickness or death as a result of poisoning. According to, soot that is coming from a heat source powered by gas should be considered a dangerous carbon monoxide risk and the heat source should be turned off until it can be inspected and serviced.

Fire Risk

Soot is a material that builds up a film over time, and it is combustible. This makes it extremely dangerous to ignore signs of soot because they could lead to a future fire. This is because soot buildup could be present in areas of the furnace that you cannot easily see. All it takes is a spark to ignite the soot in these areas to start a fire. 

Potential Causes of Smoke and Soot

Heat Exchanger Issues

Soot build-up in your heat exchanger may negatively impact how your home warms up. This could affect your energy efficiency. It is also possible that a problem with the heat exchanger is what is causing you to see soot. A cracked heat exchanger is an example of an issue that could cause soot to filtrate through air vents. Cracked heat exchangers pose the additional problem of spreading toxic exhaust fumes. 

Furnace Age

An older furnace that starts to exhibit these symptoms may be at the end of its service life. From a safety and cost of repair point of view, it may be best to replace it. An HVAC professional can provide the best cost comparison for what it would take to fix vs. replace the furnace. 

If your furnace was recently purchased, the smoky smell and soot could be indicative of the protective oil on the heat exchanger of the furnace burning off. The oil is applied during the manufacturing of furnaces to inhibit rusting. This type of burnt smell may have a strange, sweet smell to it. If a furnace does not stay on long enough after it is installed, this smell might be present when a property owner uses their furnace for the first time. It is also possible that an installation error is the culprit, which is why you need a professional to inspect your unit.

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