When your HVAC system stops working efficiently, it can lower your indoor comfort and cause unpleasant odors. While some of these smells can be fixable by switching out your dirty filter, others may require professional HVAC service.

Rotten Egg Odor

The smell of rotten eggs or sharp sulfur can indicate a gas leak. While natural gas naturally has no odor, many utility providers add mercaptan to give it a warning smell that you can easily identify. With gas-based furnaces, the leak can come from faulty burners, a failing gas valve, or a damaged supply line. For older systems, the most common cause is a cracked heat exchanger, which may have become damaged by rust or decades of wear and tear.


Moldy smells come commonly from air conditioners, but you can still run into them during the winter with your furnace. Most mustiness originates from excess water in the system and can be caused by a leak or a clog in your condensate line. When moisture can’t drain properly, it stagnates in the unit and leads to mold growth.

Burning or Smokiness

If you smell something burning or notice smokiness, your HVAC system may be overheating. It’s best to immediately turn off the unit before the damage spreads. Your system can easily overwork itself if it’s struggling with a clogged filter or hasn’t received recent maintenance. The inside of the unit can get so hot that it begins melting the protective coating off its wires. This persistent, pungent odor shouldn’t be confused with the normal, brief burning smell that comes when you kick on your furnace for the first time this season.

Superior and Affordable HVAC Service

Founded in 1968, Schmitt Refrigeration, Heating & Air personalizes our indoor comfort services to fit the needs of Evansville, IN homeowners. We provide residential heating and cooling services as well as commercial refrigeration care. Count on us for reliable indoor air quality solutions and high-quality air filter replacements too. Schedule your HVAC service appointment with us today.

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