What’s That Weird Smell? Air Conditioner Smells and What They Mean

Everyone has experienced that musty smell in the house when you first turn on the A/C after hibernation. Is that just accumulated dust blowing around? What about a rotten egg smell? Or a burning smell? Are any of these air conditioner smells harmful? Does it mean that the air conditioner needs to be repaired or replaced?

If your A/C smells bad, allow us to clear the air, so to speak.

How do I know if the smell is coming from my A/C?

Of course, if you’re smelling an uncommon odor only when the air conditioner is on and running — especially one that gets stronger the closer you get to the vents — it’s obvious the smell is coming from the A/C. But what about when you smell a familiar smell, such as a dirty diaper or cigarette smoke, but you can’t seem to pinpoint where it’s coming from? Your air conditioner may be the perpetrator in that case, too. When the A/C is turned on, other smell sources may be sucked into the air, causing you to smell the diaper pail that’s in the nursery upstairs while you’re down in the basement, for example. Likewise, if you, a friend, a family member or a former tenant smoked inside the home, the fumes could have been pulled into the evaporator coil, causing the cigarette smell to permeate throughout the house every time you turn the unit on.

Why does my air conditioner stink?

There are several potential reasons why your air conditioner stinks. In addition to the examples above, here are some of the main culprits:

Smell: Musty/Dirty Socks

Possible Source: Dust and moisture sticking on the A/C evaporator coil and filter

Smell: Mold/Mildew

Possible Source: Clogged condensate drain line (i.e., water buildup), air conditioner too big for your home (i.e., running quick-cooling cycles and not adequately dehumidifying your home’s air), general moisture buildup

Smell: Rotten Egg

Possible Source: Pest problem or dead animal in the ductwork or attic, natural gas leak near the ductwork

IMPORTANT: If you suspect a gas leak in your home, open the windows, get out of the house immediately and call the gas company. It could be a life-threatening situation.

Smell: Burning

Possible Source: Electrical/mechanical problem with the fan or compressor

Smell: Sewage

Possible Source: Backed up sewer line or ruptured vent pipe near the ductwork

Smell: Gun Powder

Possible Source: Shorted-out circuit board or fan motor

Smell: Exhaust

How do I get rid of air conditioner smells?

Luckily, most air conditioner smells occur because of a dirty or clogged air filter, and all you have to do is clean or replace the filter. Likewise, it may help to ensure your condensate line is clean and free of debris. And, of course, if you’re smelling an odor that can be found somewhere in your house (like the diaper example), it should go away when the source of the smell is removed. If, however, you’ve cleaned or replaced the filter, cleaned your condensate line and eliminated any obvious odor sources, but you’re still smelling the bad smell, you’ll need to call in the professionals. This is especially true if you suspect any leaks or electrical/mechanical issues with your unit.

Aside from performing routine maintenance on your air conditioner unit, the best way to protect your home — and your budget — from unforeseen A/C issues is to include its system components in your home warranty. That way, you can guard against the costs of covered repairs and, as a result, breathe easy.

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