Furnace Burning Smell: Causes and Fixes

HVAC Logo IconBy HVAC.comSeptember 26, 2023
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When heaters get revved up for the cold season, they can let out some unusual odors. If your furnace smells like it's burning, it’s likely not a reason to panic. However, some red flags could point to a bigger issue with your heating system. This article will walk you through the factors that play into that burning smell and when to call a pro. 

What’s causing the furnace burning smell?

There could be a number of culprits behind a burning smell. Many of these factors, like dust buildup, have a simple remedy. On the other hand, certain scents could clue you into a larger problem with your system.

Dust on the furnace

Dust burnoff is the most likely reason your furnace smells like burning. Thankfully, it’s perfectly normal.

When your heater sits unused, it collects dust. Most Americans cool their homes in the warmer months, making spring and summer prime time for dust to settle on heaters.

As your heater starts to warm up, so does the dust in and around the system. The burning dust gives off the smoky scent that you may notice when you first turn on your heater this winter.

You should notice the burning smell start to fade within a few hours. If the stench lingers, check your air filters and the area around your heater for any foreign objects.

While the burning dust scent is normal, it’s not exactly pleasant. Home comfort tools like air purifiers may help clear the smoky odor.

Debris trapped in heating system

Household items can easily fall through your vents. When foreign objects get trapped in your ductwork, they can give off a burning plastic or rubber scent.

Debris can also get into the furnace itself. Foreign objects can make the inner components dirty, leading to quicker burnout for your heater.

If your heater smells like burning plastic, turn it off right away. Next, try to see if the smell is coming from one specific vent.

If the odor is concentrated to one vent, you probably have a foreign object in your heating system. If the smell is coming from your furnace itself, you could have an overheated motor or faulty wiring. We suggest calling an HVAC technician to figure out the specific issue. 

Dirty furnace filters or air vents

A clogged filter can cause a domino effect of issues for your heater. The blower motor, a component that sends hot air through the vents, relies on a clean filter to work properly.

The blower motor works harder to push more air through the system when the air filter is dirty. This overworking can lead to overheating, which causes a burning stench. 

Plus, dirty filters can collect mold. If your home fills with a mold or mildew odor when the heat kicks on, a clogged filter may be the culprit.

The solution? Be sure to replace your filters as often as the manufacturer suggests.

It’s also best to regularly dust the vents throughout the cold season and have ductwork professionally cleaned every three to five years. If you replace the filters and the smoky or moldy scent persists, call your local HVAC technician. 

Damaged electrical wiring

Faulty wiring can create some pungent odors like gunpowder, rubber, and plastic. If you smell any of those scents, turn your heater off right away.

Most furnaces have built-in safety measures that prevent the machine from overheating. Still, these features can sometimes malfunction.

A burning, wiry scent indicates that a component of your heater isn’t working properly. Handling faulty electrical wiring is dangerous, so leave this job to the professionals. 

When you may need a furnace repair

When your heater revs back up for the winter, a mild burning scent is normal. Still, pungent or long-lasting smells indicate a more serious problem with your furnace. 

If you smell any of the odors described below, immediately shut off your heater and call an HVAC professional.

Suspicious smells

  • Gunpowder: This could indicate faulty electrical wiring or an overheated motor.
  • Rotten eggs or sulfur: If your home starts smelling like either of these, get out quickly and call your gas company. These scents are usually linked to natural gas leaks.
  • Oil: If you have an oil furnace, it may be leaking.
  • Plastic: There could be a burning piece of equipment, debris, or a foreign object in your ductwork.
  • Burning dust or smoke: This scent shouldn’t persist longer than a few hours after first turning on your heater for the season. If it does, call a professional to rule out any bigger issues.
  • Mold or mildew: If you’ve replaced your filters and the scent doesn’t go away after a few hours, call a professional. Mold inhalation is a major health concern.
  • Electrical wiring or metallic: Overheated equipment is most likely causing a metallic or electric odor.
  • Chemical odors: Your heat exchanger, the component that warms up the air in a furnace, may be broken.

Can you avoid a furnace burning smell? 

While you can’t always prevent the smoky smell of dust burnoff, our tips below will help lower your chance of a burning smell from your heater.

Try an air purifier

Air purifiers are devices that kill airborne germs like bacteria, viruses, and mold. If your heater smells like burning, an air purifier can also kill the bacteria that causes odors.

Make sure to look for an air purifier with true HEPA filters. These special filters can kill the smallest and most pesky germs, like smoke odors.

With an air purifier, you can clear out that dusty scent within hours. Still, an air purifier isn’t a substitute for calling an HVAC technician if you smell anything suspicious. 

Get an inspection 

A few weeks before you plan to turn on your furnace, call an HVAC technician. They’ll inspect your heater, and they can remove any dirt or debris trapped in the system. 

Request that your HVAC technician size your system for the proper filter. This is especially important if you plan to use a higher MERV rating. The higher the quality of the filter, the less air it allows to move. Your technician can make adjustments to the HVAC system to allow air to move effectively through the filter.

Keep your filters fresh

Generally, you should change one or two-inch-thick filters every one to three months. Three or four-inch thick filters should be changed every six months. 

Plus, replacing or cleaning your filters regularly will keep your furnace running smoothly. Most are disposable and need to be changed every 60 days. A select few are either hand- or machine-washable, so you can spruce them up between filter replacements. 

Dust and debris buildup are common sources of a burning smell from your heater. Keep your filters clean to support optimal performance from your furnace. 

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