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The A/C Guy of Tampa Bay Inc. Blog

What Are Those Odd Odors From the Furnace?


Your furnace shouldn’t smell like … well, much of anything. Neither the system itself nor the heated air it sends into your home. Basically, it should smell like your home usually does during our short winters. 

So when you notice an unusual smell—moldy, dusty, acrid, sulfurous, etc.—coming from your furnace, it may indicate a malfunction that requires professional furnace service in Tampa, FL. Please don’t hesitate when it comes to weird odors from your HVAC system, as they can sometimes alert you to a safety hazard. Even if the situation isn’t as serious as that, these odors often warn that a furnace needs repairs before it stops working.

A Rundown on Unusual Furnace Odors

Let’s take a walk through a list of out-of-the-ordinary furnace smells you might notice.

  • Dust: Most of the time, this odor isn’t a serious problem. When you turn your furnace on at the start of the season after it hasn’t worked for many months, you’ll detect a dusty burning odor from the vents. This is the smell of the dust that has collected along the heat exchanger burning off. It will go away within an hour. If you continue to smell it, it likely means the furnace is dusty and needs to catch up on maintenance. 
  • Dirty socks: This is called “dirty sock syndrome” and affects many HVAC systems. It warns that mold has started to grow somewhere in the HVAC system. This may not be a problem specific to the furnace, but you’ll still want professionals to locate the problem and fix it. 
  • Electrical burning: This is an alarming odor to notice, and it can warn of an electrical failure in the furnace’s control board, such as melting wires. (Yes, gas furnaces use many electrical components.) Another possible cause is a motor that’s burning out—you’ll probably hear a grinding noise accompanying the odor. Shut the furnace off and call technicians right away to fix this before the furnace suffers more damage or creates a fire hazard.
  • Rotten eggs: This unpleasant sulfurous smell is a warning of a gas leak in the furnace allowing unburned natural gas to escape. Natural gas does not have an odor, but the gas company puts a chemical called mercaptan into the gas to make leaks easier to detect—the rotten egg smell you’re noticing. Immediately shut off the gas to the furnace and call us to inspect the heater.
  • Smoke: When the odor of smoke starts to come from the furnace or the vents, it usually means the furnace’s flue has become blocked and exhaust gases are flooding back down into the furnace and ductwork. Shut off the furnace right away. If the smoke odor is strong, we recommend you leave your home before calling for assistance. 

Please don’t try to do any furnace investigation yourself! This can be hazardous and you’re unlikely to be able to fix the problem. Leave the work to our experienced team: we’ll keep you safe and warm. 

The A/C Guy of Tampa Bay Inc. serves our Tampa Bay family with integrity and honor. Rely on us for any furnace or other HVAC repair you need.

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