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Why Does My Furnace Smell?

As the days grow shorter and we head into October, it’s time to start turning on our heating systems again. After a cool day of apple picking, hiking, or enjoying a fall festival, you want to  enjoy a cozy evening with a furnace that doesn’t smell. If yours does smell and you’re wondering why, you’re in the right place. 

  • It’s common for your furnace to give off a smell the first time you turn it on for the heating season (it’s burning off the dust that has accumulated over the summer months). 
  • It’s uncommon if the smell is particularly strong or doesn’t go away in a few minutes. 

When your furnace smells like burning plastic or rotten eggs, or if your furnace smells musty, turn it off and call a heating expert like HVAC Comfort for service. Furnace odors can be concerning, but they’re often clues to specific issues that can be resolved with minor furnace cleaning and repair.

Let’s explore the common odors you may notice and some furnace service solutions to help you breathe easy.

You’ve Noticed a Burning Smell from Furnace

Dust and Debris Accumulation

Are you wondering why your  furnace smells when you turn it on? One of the most common reasons for a strange smell when you turn on your furnace is the accumulation of dust and debris within the heating system. Over time, dust, pet dander, and other particles can settle in your furnace, especially during the warmer seasons when it’s not in use. When you fire up the furnace, these accumulated particles can burn off, creating a noticeable burning odor.

How to stop dust and debris from entering your system: Regular furnace maintenance is key to preventing this issue. Change your furnace filter regularly (typically every 1–3 months) and consider scheduling annual professional HVAC maintenance to clean out your system thoroughly. Regular maintenance can help prevent the need for furnace repairs.

Clogged or Blocked Air Ducts

Blocked or clogged air ducts can lead to poor airflow, causing dust and debris to accumulate within your ductwork. When the furnace operates, it can push this trapped debris into your living spaces, resulting in musty or dusty furnace smells and odors.

How to avoid issues with your ducts: Inspect your air vents and ducts regularly for blockages or debris. If you notice any, remove the obstructions, and consider scheduling a furnace service, like a professional duct cleaning, to maintain clean and healthy indoor air quality.

You’ve Noticed an Electrical Smell from Furnace

Frayed Wires or Failing Motors

If your furnace is aging, issues with electrical components happen more often, which may be why your furnace smells. When these electrical parts fail, they give off an electrical smell from the furnace that smells like burning plastic. Newer furnaces may have built-in safety features that cause an automatic shutdown of the unit when there are electrical problems.

How to resolve electrical issues: Issues with electrical components always require furnace service. Immediately contact a licensed furnace repair company and have them inspect your furnace.

You’ve Noticed a Burning Oil Smell from Furnace

Dirty Burner or Combustion Chamber

If your furnace smells like burning or oil, it might be due to a dirty burner or combustion chamber. The accumulation of soot and grime on these components can lead to a distinct odor when the furnace ignites.

How to clean dirty parts: This issue is best handled with a furnace service by a licensed HVAC technician. Schedule a professional cleaning and HVAC inspection to ensure your furnace’s burners and combustion chamber are clean and functioning correctly.

You’ve Noticed the Furnace Smells Like Rotten Eggs

Gas Leak

A gas leak in your home is a serious safety concern that’s often detectable as a strong, foul odor resembling rotten eggs. Some homeowners presume the rotten egg smell is coming from the furnace, but it’s actually coming from a gas leak elsewhere in the home. Natural gas is odorless, but utility companies add a chemical called mercaptan to give it a distinctive smell and to help detect leaks.

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What to do if you smell rotten eggs: If you suspect a gas leak, or if your furnace smells like rotten eggs, do not attempt to fix it yourself. Immediately evacuate your home, leave the door open, and call your gas company’s emergency line for furnace service. They’ll dispatch a technician to investigate and repair the leak. 

Here’s what Oakland County gas utility providers have to say: 

  • DTE Energy: “Smell gas? Call 911 then DTE at 800.947.5000.”
  • PIE&G: “To report a gas emergency anytime: Call 911.”
  • Michigan Gas Utilities: “Gas odor or damaged gas line — Leave area immediately and call: 800-401-6451.”
  • Consumers Energy: “Call 9-1-1 and 800-477-5050.”

You’ve Noticed the Furnace Smells Musty

Mold or Mildew Growth

If your furnace smells musty or moldy, it could be a sign of mold or mildew growth in your HVAC system. Mold can thrive in dark, damp conditions, making the interior of your furnace an ideal breeding ground.

How to fix mold and mildew growth: Contact an HVAC professional to inspect your system for mold or mildew growth. During your furnace service, they’ll clean and disinfect the affected components and address any underlying moisture issues.


HVAC Comfort Is Oakland County’s Trusted Furnace Service Experts

A furnace smell can be disconcerting, but in most cases, it’s a problem that’s resolvable with  a minor furnace service or repair. To avoid the burning smells and other furnace repair issues, keeping up with regular maintenance, proper cleaning, and professional inspections is key. Remember, safety should always be your top priority. If you ever suspect a gas leak or are unsure about the cause of a furnace odor, don’t hesitate to seek professional assistance for furnace service. By taking proactive steps, you can ensure your furnace operates efficiently, keeping your home warm and comfortable throughout the winter months while maintaining good indoor air quality.

Originally Published: September 27, 2022

Written By: HVAC Comfort Team