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Why Your Furnace Smells and What to Do About It

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Furnace Smells


The warm air that comes from our furnaces is nice to have, especially during cold Canadian winters, but the odors that go along with it can sometimes...

Posted by Ryan | September 12, 2018

The warm air that comes from our furnaces is nice to have, especially during cold Canadian winters, but the odors that go along with it can sometimes be unpleasant. While some furnace smells are harmless others can indicate that something is seriously wrong. Here is a list of common furnace odors, their causes, and what you can do to keep your air smelling fresh and clean.

Harmful Odors

Some odors may indicate a serious problem. If you are ever in doubt you should turn off your furnace and evacuate your home before contacting a professional to assess the situation.


If your smoke detector goes off, or you smell smoke, you should shut off your furnace immediately. Smoke may indicate that your furnace’s chimney is blocked, which means that your furnace is venting smoke through your air ducts instead.

To rectify the problem you should call a professional and have your chimney cleaned. If the scent is faint you should be able to vent the smoke by opening your windows, but if the smoky smell is strong you should evacuate your house until a professional can determine the exact source of the smoke.

Burnt Electrical

The smell of burnt electrical components usually indicates that the inside of your furnace is too hot, damaging rubber or metal components. Stay safe by turning off your furnace immediately, and call a in a professional to assess and rectify the situation.


Chemical smells, particularly those that smell like formaldehyde, may mean that the heat exchanger in your furnace is cracked. The heat exchanger is responsible for moving heat from the combustion chamber into the plenum.

A broken heat exchanger is a huge fire hazard, and may also cause your furnace to leak carbon monoxide throughout your home. Turn off your furnace and evacuate immediately before calling in a professional.

Rotten Eggs

A rotten egg smell means there is likely a problem with your furnace’s natural gas supply. Though natural gas is naturally odorless suppliers treat the gas so that it has a strong rotten egg smell in order to make gas leaks more easy to detect.

Turn off your furnace immediately and contact your natural gas company. They will be able to provide your with further instructions for staying safe and ventilating your home. You should also avoid turning your furnace back until it can be assessed by a professional.

Harmless Odors

Some odors are harmless, but that doesn’t mean you should ignore them. These smells usually indicate that your furnace is in need of maintenance.


A musty smell usually indicates that there is moisture trapped inside your furnace. If this smell is faint, or dissipates after a few hours, there is no cause for concern.

However if the musty smell lasts for more than a few days it may indicate that there is mold growing inside your furnace. Some types of mold can be toxic when inhaled, so you should call a professional to come and assess the situation.

Burnt Dust

Furnaces, especially those that are located in our basements, tend to collect dust. When your furnace isn’t in use (such as during the summer months) this dust can build up on inside components. When the furnace is turned on the dust burns, creating an unpleasant smell.

Once the accumulated dust has burned away the smell should dissipate. However, if the smell persists for more than a day you should contact a professional and see if your furnace requires maintenance.

Burning Oil

The smell of burning oil usually means that your furnace filter is clogged. You should be replacing your furnace filter every three months, though if your home has pet hair, smoke, and excessive dust you should change it more frequently. Once you replace your filter the smell should dissipate.

If changing the filter does not stop the smell you should contact a professional, since this may indicate that there is an oil leak inside your furnace.

Dirty Socks

A dirty sock smell may indicate that there is a buildup of bacteria in your furnace, and is often caused by a buildup of condensation. The best way to rid your furnace of this unpleasant smell is to give it a thorough cleaning and replacing your air filter. If the smell continues to linger then the problem may be in your air ducts, which will need to be cleaned by a professional.


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Written by Ryan Tutak

Ryan is considered one of Calgary's most knowledgeable residential HVAC specialists. Working in the industry for over 12 years, he's helped thousands of homeowners with their heating and cooling systems. Outside of running Calgary's most reputable HVAC business, you can find him on the Golf course practicing his short game or traveling with his family. His main goal is to create a positive collaborative culture, one in which his employees are excited to come in and are motivated to work hard. He spends the majority of his day working directly with Home Comfort Advisors, Service and Maintenance Technicians, and Customer Service Representatives ensuring they are fully prepared to lead the Home Service Industry in Customer Service.

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