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Looking for professional heating, cooling and air quality advice? Our experts share helpful news, tips and tricks every other week! 
Advice from the Professionals
Furnace Smells To Watch Out For & What To Do Next

Bad Furnace Smells

Furnace Smells To Watch Out For & What To Do Next

If you haven’t already cranked the heat up, you will soon! Ontario’s winter forecast is in, and it’s going to be a doozy! 

With low temperatures and lots of snow, homeowners are in for it. Better make sure your furnace is ready to take the hit! 

If you sense anything amiss with your heating system, now is the time to get it fixed. 

Speaking of which…

In this article, our Campeau Heating team explores some not-so-welcome furnace smells. If you’ve yet to turn your furnace on this year, you’ll want to keep these smells in mind. They are warning signs, after all, potentially pointing to bigger issues.

It’s our mission to help you catch these furnace smells before they turn into big repair bills!


Unsafe Furnace Smells & What To Do Next

These are the furnace smells you shouldn’t ignore - they could pose a threat to your health, HVAC equipment and home!

Chemicals (Formaldehyde)

First up is the smell of formaldehyde. 

Formaldehyde is a colourless chemical with a strong, almost pickle-like odour. 

At room temperature, this chemical becomes a gas, making it a volatile organic compound (VOC). 

Burning natural gas, gasoline, wood, tobacco and kerosene all produce formaldehyde. Your system should contain the smell unless there is a crack in your heat exchanger. 

While invisible to you, formaldehyde is quickly sensed by your body or environment. 

At low levels, it can irritate your nose, eyes and throat. 

At high levels, it can pose a fire hazard and cause your furnace to leak carbon monoxide.

What To Do:

Step 1. 

  • Turn your furnace off. 

Step 2. 

  • Evacuate immediately. 

Step 3. 

  • Call a professional. 

Rotten Eggs 

The smell of rotten eggs should sound alarm bells in your mind. This furnace smell is one you should always be aware of and on the watch for. 

Natural gas is a highly flammable material that can cause a huge fire hazard and gas poisoning. 

Because natural gas is odourless, suppliers treat it with something called mercaptan. Mercaptan is what gives off that distinctive rotten egg smell.

They treat the gas so a leak can be easily and quickly detected.

What To Do:

Step 1. 

  • Evacuate immediately. 

Step 2.

  • Call a professional and/or the fire department right away. 


If your furnace smells like smoke, this could mean you have a blocked chimney. If this happens, your furnace could start venting smoke through your air ducts and into your home! 

What To Do:

Step 1.

  • If the smell is faint, call a professional and open windows in your home to increase ventilation. 

Step 2. 

  • If the smell is strong, evacuate your home and then call a professional to handle the issue.

Burnt Electrical 

A burnt electrical smell could point to:

  • An overheated furnace.
  • Damaged rubber components.
  • Damaged metal components.

Each of these potential issues poses a safety risk in your home. So don’t ignore it! 

What To Do:

Step 1. 

  • Turn off your furnace right away. 

Step 2. 

  • Call a professional. 

Hot Metal

The smell of hot metal is like that of burning electrical. But typically, it has more of an iron scent.

This smell could point to an electrical issue or an overheating problem. 

What To Do:

Step 1. 

  • Call a professional. 

Burning Plastic

If your furnace smells like burning plastic, there’s typically a very obvious culprit in the way. 

The smell of burning or melting plastic typically points to exactly that - a piece of plastic next to or touching your furnace. 

It could be something as small as a dog toy left too close to your system!

What To Do:

Step 1.

  • If safe to do so, remove the plastic. If not, call a professional to do it for you!


Harmless Furnace Smells

These are the smells that you don’t need to worry about - they’re completely harmless! 

In most cases, these smells are natural to furnace operation. But if any of these smells are new to you or make you uncomfortable, we highly recommend giving us a call.

Our priority is always your safety, comfort and peace of mind. And our furnace experts work with these systems all day, every day. We know them in and out! 

We’ll let you know if the smell is safe or if it has escalated into something harmful. 


Musty furnace smells are typically nothing to worry about. The cause is usually moisture trapped inside your furnace. This moisture and smell should both dissipate in a few hours.

If, however, the smell does not leave after a few hours, it may mean you have mould growing in your furnace. 

Because mould can be toxic, you should monitor this smell the minute you sense it. 

What To Do:

Step 1. 

  • If the smell lasts more than a few hours, call a professional. 

Burning Oil (Diesel)

The smell of burning oil typically points to a clogged furnace filter. Thankfully, this is one of the easiest smells to fix - all you need is a new filter!

Related Article: How To Choose and Care For Your Furnace Filter 

We recommend changing your furnace filter every 90 days. If you have a large family or pets, this could increase to every 30-60 days!

What To Do:

Step 1. 

  • Change your furnace filter. If this doesn’t work to get rid of the smell, call a professional. 

Burnt Dust 

The smell of burnt dust is very typical if you've just powered on your furnace. 

Over the summer, the system’s been sitting in the basement, collecting dust. When turned on again, that dust then begins to burn away. No wonder you can smell it throughout the house!

Don’t worry. It usually only takes a few hours for the smell to leave. 

What To Do:

Step 1. 

  • Let your furnace run until the smell dissipates. If that doesn’t work, call a professional.

Dirty Socks

If you’re smelling dirty socks, your nose probably isn't far off from the truth. 

This smell typically indicates a buildup of bacteria in your furnace.

This buildup is usually caused by a buildup of condensation - causing a repulsive odour. 

What To Do:

Step 1. 

  • Schedule a furnace cleaning and replace your filter. If this doesn’t work, book a duct cleaning! 


Trust Your Nose - Give us a call!

When it comes to weird furnace smells, you have to trust your nose. While many smells aren't a cause for concern, others could put you and your family at risk. 

Keep the above list handy this winter! You never know when you might need to reference it. 

We also encourage all our Sudbury homeowners to invest in preventative furnace maintenance. 

During this visit, we ensure your furnace is ready for the harsh season ahead. We do our best to lower the rest of furnace breakdowns, leaks and other untimely repairs.

Give our Sudbury heating team a call at 705-560-2441 or contact us online!

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