Have you noticed any unusual burning smells coming from your furnace? If so, it could indicate that your furnace has major issues that you need to have repaired. There are a number of different reasons why this can happen, and here is everything you need to know about the potential causes and how to overcome them.

Issues That Can Cause a Furnace to Produce Burning Smells

Not all burning smells coming from your furnace or out of your vents are something you need to worry about. If you’re just turning your furnace on for the first time this year, it is completely normal for it to produce a burning smell for a few seconds after it first starts up. This can also occur any time your furnace has sat without running for more than a few days.

When a furnace sits unused, dust and debris can start to collect on the burners and the top of the unit. Once the furnace is finally turned on, all of that dust will quickly burn away and you will often notice a distinctive burning smell coming out of your vents. This smell will typically go away within a few minutes at the very most, in which case you have nothing to worry about.

If you continue to smell that something is burning for more than a few minutes, then this is something you need to worry about and you should immediately shut off your furnace and contact a professional HVAC technician. The same is also true if you notice a burning smell at any time other than when your furnace has sat unused.

In these situations, the burning smell usually indicates that your furnace is overheating or there are issues with its electrical wiring. Oftentimes these two problems are directly related.

If a furnace overheats, the high temperature can cause the insulation surrounding its wiring to begin to melt, and this will result in a burning smell circulating throughout the ductwork and into every room in the home. This problem has the potential to cause an electrical fire or seriously damage your furnace.

If the temperature gets too high, it has the potential to crack the heat exchanger inside your furnace. This is a serious problem that can allow combustion fumes to seep out of the furnace into the rest of your home and could lead to potentially fatal carbon monoxide poisoning. This is why it is important to leave your furnace turned off until you can have it professionally inspected. Most furnaces have a safety mechanism that will automatically shut the system off if it starts to overheat. However, this doesn’t always work and issues can still occur before the unit shuts down.

Burning smells can also occur because of issues with the HVAC blower. The smell could mean that the blower is overheating or that its motor has started to wear out. It could also be that the bearings have started to dry out and need to be lubricated. In some cases, the blower can become loose and start to grind against the metal housing, and this can also result in a metallic burning smell.

What Causes a Furnace to Overheat?

Furnaces can overheat for several different reasons, most of which are related to a lack of airflow due to ductwork issues or some other problem. In many cases, the issue is caused by not replacing your furnace filter often enough. Furnace filters need to be replaced or washed at least once every 30 to 90 days. If the filter isn’t replaced, all of the dust and debris that it traps can eventually cause it to become clogged and prevent air from being drawn through it.

Whenever your furnace is heating, the HVAC blower is constantly drawing cold air into the system through the return air vents. This cold air is then forced through the filter and into the furnace. The cold air then flows into the heat exchanger, which takes the heat energy from the combustion chamber and transfers it to warm up the air. If the filter is clogged and not enough cold air can be drawn into the furnace, it leads to all of the heat remaining inside the combustion chamber. This can quickly cause the temperature to become too hot and lead to the furnace overheating. The same issue can also result if the return air vents are obstructed or clogged with hair and debris.

Similar issues can also occur if your supply vents are closed or clogged, or if there is any furniture in front of the vent that blocks the airflow. In these situations, the heating system won’t be able to circulate heat out of the furnace quickly enough. This will lead to the temperature rising and eventually cause the furnace to overheat.

Other Furnace Smells to Watch For

Furnaces can also produce other unusual smells that can be a sign of some other problem. One of the biggest ones to watch out for is anything that smells similar to rotten eggs. If you do notice a rotten egg or sewage odor coming from your furnace, it means that there is natural gas leaking from either the furnace or the gas line that feeds into it.

This is obviously a serious issue that has the potential to cause a major explosion and could destroy your house. If you suspect that you have a gas leak, you need to take immediate action to have it repaired. If you only notice a faint rotten egg smell, this indicates that the leak is fairly small. In this case, you should simply shut off the gas to the furnace until you can have it inspected and the leak repaired.

A strong rotten egg smell near your furnace or coming out of your vents is a sign that you have a major leak. In this case, you should immediately close your main gas shut-off valve and then get yourself, anyone else in the building and your pets out and away from the home. Before leaving, quickly open up at least a few windows to help the gas dissipate and reduce the chances of an explosion. Once you are a safe distance away from the house, you should then call the fire department or your gas provider’s emergency line to report the leak. After reporting the leak, stay far away from the building until your gas is shut off and the leak is fixed.

Chemical odors coming from your furnace can also be a sign of a serious issue and usually mean that your heat exchanger is cracked and combustion fumes are leaking out. It could also be that the exhaust vent is clogged or damaged, which can also cause combustion fumes to back up inside the home.

Carbon monoxide doesn’t have an odor, but some of the other combustion fumes produced by a furnace have a distinctive chemical smell similar to formaldehyde. Due to the potential for carbon monoxide poisoning, this is another issue that you should have checked out immediately, and you should not attempt to run your furnace until it has been inspected and you know it is safe to use.

If you notice any unusual smells coming from your furnace, the experts at All Tech Heat & Air are always here to help. Our certified HVAC technicians specialize in furnace repairs and maintenance and can quickly inspect your furnace to determine what the issue is. We also work on and install air conditioners and geothermal HVAC systems for customers throughout the Oklahoma City area. Contact us today if you have any questions or need to schedule a furnace inspection.

Dan Addi
Dan Addi

Director of Operations

Dan Addi is the Director of Operations for All Tech Heat & Air, and has 20 years of experience.
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