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Why Does My AC Smell Like…

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You expect your air conditioner to send clean, fresh-smelling air into your home, keeping you and your family comfortable. Unfortunately, sometimes the air coming from those vents doesn’t smell fresh at all. Some of the causes of those smells are relatively harmless, while others require immediate attention to prevent hazards to your health and home. Here are a few of the most common odor problems we see with air conditioners, and what they usually mean:





The most common cause for an unexplained fish odor in the home is not mold or dead animals in the crawlspace, as many people might think. Instead, it is overheated plastic in electrical components. The plastic used in these components contains a chemical that emits a fish or urine-like smell when it gets extremely hot or burns. The ultimate source of that fish smell in your home could be one of many things—an outlet, a switch, an electrical breaker, wiring, even an overloaded extension cord.

The reason that the smell seems to be coming from the HVAC system is usually that the odor is being drawn in through the intake vent, then dispersed through the home, although it is possible that the electrical issue is occurring inside the heater or air conditioner itself.

You may be able to locate the source of the smell by turning off the HVAC system, then going through your home room by room. If there’s no odor at all when the HVAC is turned off, the problem may be in the HVAC. On the other hand, if some part of the house still smells “fishy” even when the HVAC isn’t running, then that may be where your electrical problem is happening. You can further try turning off lights and unplugging appliances to narrow down the source of the odor.

Whether the odor is coming from your HVAC system or from another source in your home, overheating electrical components clearly pose a serious fire hazard. So if you smell a fishy odor, don’t simply hope that it will go away. Contact a licensed electrician or HVAC technician to fix the problem before it results in something much worse than a big stink.


If your AC smells like gunpowder when it first comes on, that could be a sign of an electrical component that has burned or shorted out. As with the fish odor, you should call for service immediately to prevent further damage to your system and potentially to your home.

Rotten Eggs or Sewage

Both of these odors can be signs of potentially dangerous situations. If you have natural gas running to your home, a rotten egg smell could be a sign of a natural gas leak. The safest course is to get out of your house and call the gas company immediately.

Another potential cause of a sewage smell coming from your AC vents is a sewage leak located somewhere near the air ducts. The methane gas from the sewage can leak into the ducts and get into your conditioned air that way. Again, this is a problem that requires immediate attention.

Dirty Socks or Stinky Feet


If the air coming from your AC smells musty or like it’s been drawn directly from a locker room, the problem is most likely related to mold or bacteria growing inside of your HVAC system. One common culprit is a clogged drain line. When the drain line gets clogged, water backs up in the drain pan, creating a perfect dark, wet environment for mold and bacteria to grow. If that’s the problem, your trusted HVAC specialist will need to clear out the clog and clean the drain pan.

Another possible cause for the stinky feet smell is mold growing on your evaporator coils or in your air ducts. Having your evaporator coils checked annually as part of routine maintenance and cleaned as needed can help to prevent this problem. If it’s not caught early, the evaporator coils may have to be completely replaced. Mold in the air ducts will also require professional cleaning, and possibly replacement depending on the extent of the mold.

It’s important to have mold cleaned out in a timely manner because otherwise, it will continue to grow and spread throughout your home. And that won’t just cause a bad smell. Mold can cause a range of respiratory symptoms, especially in people with allergies or asthma. If you have a dirty sock smell in your home, get it checked out by a licensed HVAC technician before it gets worse.

Rotting Garbage

If your home starts to smell like a garbage can that’s been sitting in the sun for a couple of days, then you’ve probably got a dead animal somewhere in the house. Not only can wildlife get into your crawlspace or attic and die, sometimes critters can get inside of your HVAC unit or air ducts. Mice, rats, and squirrels are some of the most common culprits, but occasionally something larger like a raccoon or possum can even get in there. Or snakes!

In order to get rid of the odor, the dead animal will need to be removed, then the HVAC system will need to be cleaned. Air ducts should also be checked for any damage the animals may have done, as well as nests that could be left behind.

Cigarette Smoke


If the air coming out of your air conditioner vents smells like cigarette smoke even though no one is smoking in the house, it probably means that the previous owners were smokers. The condenser coil can actually absorb cigarette smoke odors and release them when it runs later on. You’ll need to have the coils cleaned by an HVAC specialist to remove the smell. (If you’ve just moved in to the house and haven’t changed the air filter yet, try that first, because the filter can also absorb those odors.)


A chemical-type smell from your AC can have several different causes. If you’ve just had new ductwork installed, it could simply be the smell of the glue from the ducts, which will fade over time. Another common cause is open or leaking bottles of chemicals, such as cleaners, sitting near the indoor unit of the AC. Removing those chemicals from the area could solve your problem. However, the other possibility is that your air conditioner is leaking refrigerant and that’s what you’re smelling. In that case, you’ll need to call your licensed HVAC specialist to seal the leak and recharge your air conditioner.

In Conclusion

Any smell coming from your air-conditioner could be cause for concern. Calling and having it checked out is always a good option.