Technician using vacuum to clean dust from inside of furnace

Why Does My Furnace Smell?

Like any appliance, your furnace requires routine maintenance and cleaning. It’s not uncommon to notice the smell of burning dust emitting from your furnace or heater at the beginning of heating season—this is typically an indication of a unit in need of cleaning. But some smells may be warning signs of a larger, more dangerous problem. If you ever smell odors of gas, burning plastic, or sulfur, it’s time to bring in the pros.  

What Do We Mean by Furnace Odors?  

The first time you turn on your furnace for the cold season, the chances are you will smell something. That smell is typically burning dust pushing its way through your ducts. The distinct smell of dust or burning dust should dissipate in a matter of hours.  

Other odors may indicate a dangerous problem with your unit. Odors of burning plastic, gas, sulfur (or rotten eggs), or mildew should not be written off as a short-term inconvenience. The problems these odors may indicate leave a lasting impact on your health. 

Related TopicWhy Does My House Smell Musty? 

My Furnace Smells “Funny” 

“Funny” odors may be localized around your furnace, but it’s more likely that you’ll detect the smells throughout your home as the HVAC unit circulates warm air. The most common “funny” furnace smells are often referred to as burning dust, must, rotten eggs, and burning plastic.  

  • Burned Dust: Like all spaces in your home, dust, dander, pollen, and mold spores may collect on the inside and outside of your unit and throughout your HVAC duct work. This is especially true of homes that do not have central air. It’s not uncommon to smell dust or burning dust when the heat is first turned on for the season.  
    While dust is less dangerous than some of the other odors you may detect from your central heating system, circulating dust particles will have a direct impact on the indoor air quality (IAQ) inside your home. Poor indoor air quality has been linked to many common health conditions. Engaging in professional furnace maintenance and cleaninginstalling an air filtration system, and having your air ducts cleaned every three to five years can and will help improve the quality of the air your family breathes.  

  • Must: A musty smell may indicate a number of issues, including a problem with your central air conditioner condensate drain line, a furnace humidifier filter in need of replacement, or mold and mildew growth inside your unit or air ducts.  
    Like dust, mold and mildew may have a negative impact on the health of your loved ones. If you suspect mold growth is happening in any part of your HVAC system, it’s important to work with a professional to remove the mold and remediate the space. 

  • Rotten eggs: Odors of sulfur (often described as rotten eggs) may indicate a gas leak in your home. Propane and natural gas are both colorless and odorless. Energy companies are required to add a chemical, mercaptan, to natural gas and propane gas supplies so that a leak may be detected more easily.  

  • Burning plastic: It’s possible that a brand-new furnace or central heating system may emit an odor of burning plastic for a short period of time after installation. However, an existing unit should never smell like burnt or burning plastic. This may indicate that your system is overheating or that components are wearing against each other. Any HVAC system that smells like burning plastic should be inspected and repaired by an HVAC technician.  

Is It Normal to Smell Gas Near a Furnace? 

No. Mercaptan smells may mean disaster for your home. Gas leaks are incredibly dangerous and should be addressed immediately. 

If you suspect a gas leak in your home, it’s important to:  

  • Turn off any gas-powered appliances.  
  • Evacuate all pets and people from the premises (leaving any doors and windows open as you exit).  
  • Call 911. Emergency personnel will assist in shutting off the gas supply and investigating the space.  

Once your home is safe, work with a reputable HVAC technician to repair or replace your unit. We offer emergency HVAC services to help homeowners like you recover from HVAC disasters.  

What Should I Do When I Notice a Weird Smell Coming from My Furnace? 

Ultimately, weird or funny smells coming from your HVAC system are warning signs, signaling potential danger. Furnace odors are not a time for DIY solutions. To protect the safety of your household, any odors should be addressed and resolved by a licensed professional in an urgent manner.  

Related TopicSigns You Have Poor Indoor Air Quality 

My Furnace Smells Musty: What’s Next?  

A musty furnace may indicate a problem with a clogged condensate line or furnace humidifier, causing mold growth. Mold originating in a furnace or in duct work may quickly spread throughout a home as spores travel through air ducts.  

Mold growth in your furnace may indicate a problem with indoor humidity levels or hidden water damage. Suspected mold or water damage should be addressed immediately. Your local Aire Serv® can inspect and clean your HVAC system.  

If we uncover water damage, our technicians may refer you to fellow Neighborly® company, Rainbow International®, for professional water damage restoration.   

Your furnace could smell musty for a few reasons. If your furnace is new, it could just be burning some chemicals off as you begin its use. If your furnace is older, it may be time to address a duct cleaning service or add a humidifier to your unit. If you have a humidifier, your filter could be dirty, which can negatively impact the indoor air quality of your home. If you have changed filters and cleaned your entire furnace and duct work and your house still smells musty, you could have a bigger problem than your HVAC unit. You could have hidden water damage in your home, which can cause mold growth and a musty smell. To help identify the moldy culprit, reach out to our colleagues at Rainbow International

Is It Normal for a New Furnace to Smell? 

Please don't panic. A newly installed furnace may give off an unpleasant smell when you use it for the first time. The smell after you turn on your new furnace is the protective oil coating on your new heat exchanger. It should burn off, and the smell should dissipate within an hour or so. If the smell persists for more than a day, consult your HVAC technician. 

Stay Safe! Address Furnace Smells Swiftly  

If you smell anything out of the ordinary, don't wait—contact your HVAC specialist immediately. Be proactive! Before you even smell anything funky, contact your HVAC specialist and schedule routine maintenance. Your local Aire Serv technicians will be able to assess any problems before they even start! Request an estimate online today or call (855) 679-0011.