Your HVAC system’s primary functions are to control air temperature and airflow — not air odors. And from time to time, you might notice that the air flowing out of your vents smells a little off.

Particular odors are harmless and temporary, while others can be persistently infuriating or may even signal a serious problem with your system. Pay attention to these odors when you notice them, and be sure to take action if it’s a cause for concern.

Do You Smell Smoke?

A sudden and unexplained smell of smoke coming from your vents is almost always a bad sign, and can often be traced back to some electrical or mechanical problem in the A/C unit. Moving parts like the fan and motor have the potential to overheat, seize up or even catch fire if the unit hasn’t been properly maintained.

If you can smell something burning and you think the odor is flowing through your vents, shut off your HVAC system at the thermostat and check the unit outside. If you can smell or see any smoke coming from the condenser, keep the system turned off and call a repair professional immediately.

Tobacco Smoke

If someone smokes tobacco in a home, the HVAC system will circulate that smoke throughout the home — including inside the system itself. The smell of stale smoke can become attached to the condenser coils and leave an odorous film inside ventilation ducts. This can be hard to notice if you’re living with a smoker, but is most often an issue when a non-smoking family purchases a home from a family with a smoker.

HVAC professionals have special cleaning methods they can use to clean ductwork, which should help control the odor. Deodorizing coils can be more difficult, but thorough cleaning and maintenance can make a huge difference.

Damp and Musty

If the odor coming from your vents smells like mildew and mold, the bad news is that’s probably exactly what it is. Mildew and mold can also form on coils and in ductwork, and left untreated, it can spread to other parts of your home. There are several potential causes of this problem, including blocked drainage tubes, leaky ductwork, and insufficient insulation. It’s important to correct the underlying problem before moving on to cleanup.

Cleanup is critical, because mildew and mold spores can be circulated all over your home by your HVAC system. This doesn’t just create a musty smell — it’s a health hazard.

First Heat of the Season

The first time you fire up your furnace for winter, it’s normal for an unpleasant smell to fill the home. But this is normal and harmless — dust settles on your furnace’s heating elements all summer, and when you turn the system back on, that dust burns up. Open a few windows, and the smell should clear quickly.

If you smell these or other odors coming from your vents and you’re not sure what to do, don’t worry. Your skilled, local HVAC technicians have seen it all before, and they’ll get the problem solved as quickly as possible.