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Why Your Furnace Smells & What to Do About It

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Air Quality, Furnaces

Canadian winters can be tough, and you’ll need your trusty furnace to keep your home warm and cozy throughout these frigid months. However, sometim...

Posted by Ryan | July 2, 2023

Canadian winters can be tough, and you’ll need your trusty furnace to keep your home warm and cozy throughout these frigid months. However, sometimes you might notice unpleasant odours wafting out along with the warm air. While many of these smells are fairly harmless, others can be warning signs of a serious problem.

Fortunately, the Action Furnace team has performed enough furnace repairs throughout Calgary to know the difference, and we’re here to show you too. Let’s delve into common furnace smells, their causes, and what you can do about them.

When to Be Concerned: Harmful Odours

Some smells emanating from your furnace can signal serious—even potentially hazardous—issues. If you’re uncertain, it’s always best to err on the side of caution: turn off your furnace and leave your home until one of our professionals can assess the situation.


If you notice a smoky scent or your smoke detector is activated, it’s crucial to switch off your furnace right away. This could be a sign of a blocked chimney, causing smoke to vent through your air ducts instead. The next thing you should do is call us for help.

If the smoky smell is mild, opening windows can help ventilate your home. However, if the smell is strong, you should evacuate your house until our team can identify the source. Even when there’s only a mild smell, it’s still best to have us inspect your furnace during a routine tune-up so we can tell you if it has the potential to get worse.

Technician servicing furnace to repair or replace damaged components causing burning smell

Burning Rubber or Plastic

If there’s a burning smell, it may mean that your furnace is overheating and causing damage to sensitive components. Ensure your safety first by turning off your furnace immediately—then call us to identify the damaged components and repair or replace them if necessary.


Chemical odours, especially those resembling formaldehyde (a strong smell that many people describe as being similar to pickles), could imply a cracked heat exchanger. This is the part that transfers heat from the combustion chamber into the plenum and is responsible for making sure exhaust gas can be safely vented out of your home.

A broken heat exchanger is a significant fire risk and could lead to carbon monoxide leakage. In this case, turn off your furnace, evacuate your home promptly, and call us immediately—this is a case where emergency furnace repairs are warranted.

Service technician tightening gas line to help prevent leak

Rotten Eggs

If you detect a rotten egg smell, this could indicate an issue with your furnace’s natural gas supply. Since natural gas is naturally odourless, suppliers add a rotten egg smell to help detect leaks. Gas leaks can be incredibly dangerous, as they can result in explosions if the gas comes into contact with a flame capable of igniting it.

If you smell rotten eggs in your home, turn off your furnace immediately and contact your natural gas company. Until one of our professionals has assessed your furnace, do not turn it back on for any length of time.

When Not to Worry as Much: Harmless Odours

While the following smells are largely harmless, they still shouldn’t be ignored—as they often indicate your furnace requires maintenance. Leaving these issues alone could be costing you money every month on your heating bills by reducing your furnace’s efficiency, so it’s still best to call for help if you notice them.


A musty smell usually signifies moisture trapped inside your furnace. If the smell is mild or disappears after a few hours, there’s likely no need for concern. However, if the smell persists for several days, it could indicate mould growth inside your furnace. As certain moulds can be hazardous when inhaled, you should have your furnace inspected and cleaned if necessary.

Burnt Dust

When your furnace is not in use, dust can accumulate inside. When the furnace is turned back on, this dust burns off, creating an unpleasant smell. The smell should disappear once the dust has burned away. If it lingers, something else might be burning (see above) that could indicate a more serious problem.

Pet lying on return vent to signify furnace that needs air filters changed more often

Burning Oil

The smell of burning oil usually signals a clogged furnace filter. Regularly replace your furnace filter on a monthly basis to avoid this as a rule of thumb. However, if your home has pets, smoke, or excessive dust, you might need to change it more often. If the smell continues after changing the filter, contact us as this could indicate an oil leak inside your furnace.

Dirty Socks

A dirty sock smell could mean a bacterial buildup in your furnace, often caused by condensation. A thorough cleaning of your furnace and replacing your air filter usually solves this issue. If the smell persists, you might need duct cleaning.

Air filter being replaced in central furnace to eliminate odour

Frequently Asked Questions About Furnace Odours

What Does Furnace Exhaust Smell Like Normally?

Typically, furnace exhaust should not have a noticeable smell. If there is a scent, it should be relatively neutral or faintly metallic due to the normal combustion process.

Can a New Furnace Have Weird Smells?

Yes, it’s possible for a new furnace to emit a metallic or oil-like smell initially as it burns off residue left from its manufacturing process. This should dissipate after a few uses. However, if the smell persists, it’s advisable to call a professional.

Is There a Way to Make My Furnace Smell Better?

Regular maintenance is the best way to keep your furnace smelling fresh. This includes changing your furnace filter regularly, cleaning your ductwork, and scheduling routine furnace inspections. Using high-quality air filters and considering an air purifier for your home can also help control odours.

How Often Should I Have My Furnace Serviced?

We recommend having your furnace serviced annually, ideally before the start of the heating season. Regular maintenance can help ensure that your furnace runs efficiently, lasts longer, and reduces the risk of unexpected breakdowns during the cold months. Annual service is also important to check for potential safety issues such as carbon monoxide leaks.

Your furnace is crucial to your home’s comfort, especially during the cold seasons. By staying alert to any unusual smells, you’ll ensure the safety and efficiency of your heating system. If in doubt, never hesitate to call in a professional from Action Furnace—we’re here to keep your furnace running smoothly and your home warm and cozy.

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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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