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Bad Furnace Smells and What They Mean

Man near an air vent

A furnace is an essential component of your home’s heating system. While no unusual activity should be ignored, it is especially important to identify weird smells that may be coming from your furnace. A foul odor is a sure sign that something is wrong. Here are a few smells to be aware of and what you should do if you notice them.

Furnace Smells to Be Aware Of

Air vent on a wall
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According to Traci Fournier, VP of Operations at One Hour Heating & Air Conditioning, modern furnaces should be odor-free. If you do smell something odd, you should get your furnace checked right away. These smells mean something is wrong.

Rotten Eggs

A case of rotten eggs

A smell of rotten eggs or sulfur near your furnace could indicate a leak in the natural gas line, said Fournier. As natural gas is odorless, gas companies often add a chemical that gives off this smell to alert homeowners of potential leaks.

Inhaling natural gas can lead to dizziness, nausea, and other health problems. If you detect this smell, immediately open all windows, shut off your furnace and leave the house. Contact a professional to investigate and fix the issue.


Mold in the corner of the plastic windows.
Afanasiev Andrii/Shutterstock.com

If you smell mold or mustiness from your furnace, it likely means that there is mold growth or moisture accumulation inside the unit, Fournier said. This can be caused by a variety of factors, including leaks, high humidity, or poor ventilation.

It is important to address this issue as soon as possible, as mold can cause health problems and can also damage the furnace itself. You should have a professional inspect and clean the furnace to identify the source of the problem and properly address it.

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This all-purpose cleaner is safe to use on many surfaces, including HVAC appliances.


Dust bunnies on the floor

Sometimes when you turn on your furnace, you may notice that it smells dusty. This is likely due to, well, dust. Specifically, your furnace filter may be clogged.

Furnace filters are designed to remove dust and other particles from the air that circulates through the furnace, but they can become dirty and clogged over time. If this happens, those particles can circulate through the furnace and be released into the air.

You should replace your furnace filters at least every three months, although if there are pets or people with allergies in your home, you should do it more frequently. If a dusty smell persists after replacing the filter, it may be a sign that deeper cleaning is necessary.


A vent with smoke coming out

A burning smell coming from your furnace could mean a few different things, but it likely points to the fact that something is burning in your furnace. There may be a problem with the burners themselves or debris may have accumulated inside.

If you can’t pinpoint the cause immediately, you should contact an HVAC professional for help.

“Any malfunctioning furnace, regardless of its age or anything else, should be shut down until it can be evaluated by a qualified service technician,” said Fournier.

A Note About Carbon Monoxide

A carbon monoxide detector
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One of the most dangerous problems creating by a malfunctioning furnace is carbon monoxide gas, Fournier warned. Carbon monoxide (CO) is a colorless, odorless gas that is produced when fossil fuels such as gas, oil, and propane are burned. Furnaces and other heating systems that use these fuels can release CO into the air if they are not functioning properly.

Make sure that you have a carbon monoxide detector on every floor of your home. Being exposed to this gas for too long can cause serious health issues and even death. A carbon monoxide detector can keep you and your family safe, even if you can’t smell the gas yourself.

First Alert CO400 Carbon Monoxide (CO) Detector

Make sure your home has at least one.

How to Avoid Furnace Problems

An HVAC worker at a home
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Scheduling regular tune-ups and maintenance is the easiest way to prevent major furnace issues in the long run. Fournier also recommends changing your filters regularly, as well as making sure your home is well-insulated so your furnace doesn’t work harder than it needs to.

Furnace smells can indicate a variety of issues, from minor to serious. It is important to pay attention to any unusual smells coming from your furnace, as they can signal a problem that needs to be addressed. Here are a few to be aware of, and what to do when you encounter these HVAC issues.

Anne Taylor Anne Taylor
Anne Taylor is a writer with a BA in Journalism and a passion for storytelling. Her work has been published on a variety of websites including Mental Floss and Well + Good, and she recently published her first novel, What it Takes to Lose. When she's not writing, Anne loves to travel (19 countries and counting), spend time outside, and play with her dog, Pepper. Read Full Bio »
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