Stay safe this fall and winter – call Thomas Hoffmann Air Conditioning & Heating for furnace maintenance and repair needs.
As fall turns into winter in St. Louis, homeowners start firing up their furnaces for the first time in months. And that’s when it hits you—that strange smell coming from your vents. Should you be worried? Is it dangerous? Or is it just part of regular furnace operation?
At Thomas Hoffmann Air Conditioning & Heating, we get calls every year from concerned homeowners wondering what those furnace odors mean. The truth is, some smells are harmless while others can signal serious problems. Let’s break down five of the most common furnace smells and what you should do if you notice them.
1. Burning Dust Smell
What it smells like: A dusty, burnt odor when the furnace first kicks on for the season.
What it means: This is one of the most common smells and typically nothing to worry about. Dust collects on your furnace’s heat exchanger and burners during the summer months. When you turn it on for the first time, that dust burns off.
What to do: The smell should go away within a few hours. If it lingers for more than a day, it may be time to check your air filter or schedule a professional furnace cleaning.
2. Electrical or Metallic Smell
What it smells like: Overheating wires, melting plastic, or a metallic tinge.
What it means: This could signal an issue with electrical components, such as the blower motor or wiring. It may be overheating or malfunctioning, and continuing to run your system could cause further damage—or even a fire hazard.
What to do: Turn off your furnace immediately and call our certified technicians. Electrical smells are a serious red flag and should be addressed quickly.
3. Rotten Egg or Sulfur Smell
What it smells like: Strong rotten egg or sulfur odor.
What it means: This smell is associated with a natural gas leak, which can be extremely dangerous. Gas companies add a sulfur-like odorant to natural gas to help detect leaks, since the gas itself is odorless.
What to do: Evacuate your home immediately. Do not use any electronics or turn on/off light switches. Call your gas company from outside, then contact Thomas Hoffmann Air Conditioning & Heating for a system inspection once it’s safe to return.
4. Musty or Moldy Smell
What it smells like: Damp basement or mildew-like odor.
What it means: If your furnace or ductwork smells musty, it could be a sign of mold or mildew buildup—often due to excess humidity or a clogged drainage system in your HVAC setup.
What to do: Musty odors can impact your home’s air quality and aggravate allergies or asthma. We recommend scheduling an HVAC inspection and duct cleaning to locate and eliminate mold sources.
5. Chemical or Formaldehyde Smell
What it smells like: Sharp, chemical-like odor (similar to paint thinner or glue).
What it means: This could indicate a cracked heat exchanger, which is a serious issue. A damaged heat exchanger can release carbon monoxide into your home, posing a risk to your household.
What to do: If you smell something chemical and your carbon monoxide detector goes off—or you feel dizzy or nauseous—leave your home immediately and call us for emergency service. Heat exchanger issues require immediate professional attention.
Don’t Ignore That Smell — Call Your Local Furnace Experts
We know how important a safe, warm home is—especially during cold St. Louis winters. At Thomas Hoffmann Air Conditioning & Heating, our licensed technicians are here to help diagnose and fix furnace problems fast. Whether it’s a strange smell, a noisy blower, or a system not heating right, we’ve got your back.