Harmless AC Smells and What They Mean

Ductless split unit mounted on red wall
Last updated: 9/16/2023 

Sometimes when a home air conditioner smells bad, the problem is hazardous to your health. In this case, you should refrain from running the AC until a professional can take a look. Other AC smells are more innocent, but you may still want to address them promptly to prevent your home from stinking. Here’s a look at some of the most common harmless AC smells and what they mean.

Musty Odor

If your home starts to smell musty when you run the air conditioner, this could mean mold or mildew is growing somewhere in the system. This shouldn’t come as much of a surprise because AC units remove excess moisture from the air as they cool.

The dehumidification process causes water to collect on the evaporator coils, where it drips into the drain pan. Moisture can also linger on the air filter or in the ductwork. If excess water doesn’t evaporate or drain away, mold can start growing within just 24 to 48 hours, causing the signature musty odor to develop.

The best way to eliminate this AC smell is to replace the air filter and ensure the drain pan is emptying properly. If your efforts aren’t enough, call an HVAC professional to perform a thorough cleaning.

Stinky Feet

Stagnant water sitting in a clogged drain pan can cause the smell of stinky feet. It won’t hurt you, but you don’t want this odor circulating around your home! Plus, standing water quickly leads to mold growth.

Start by replacing the filter and unclogging the drain pan if possible. If it appears that moisture is building up somewhere else in your system, have a professional check it out.

Rotting Garbage

It’s possible for a small bird or rodent to find their way into your air ducts. If the animal gets stuck, it could die and begin decomposing. Then, every time the AC runs, it blows the smell of rotting garbage into your home.

This thought might make you queasy, but a dead animal in the ductwork isn’t particularly dangerous. Still, you undoubtedly want a professional to remove the decomposing remains as soon as possible.

Old Tobacco Smoke

The smell of stale tobacco smoke coming from your AC vents is quite unpleasant, but the source is innocent enough. All this odor means is that the condenser coil and air filter have absorbed old cigarette smoke. If you’re a heavy smoker, it’s important to schedule regular maintenance to prevent smoke residue on the coils from causing performance problems.

You’re unlikely to notice this AC smell if you’re a smoker yourself, but if a non-smoker purchases a house from someone who smokes a lot, the stench is very obvious. Fortunately, a good cleaning and air filter replacement are typically all you need to eliminate old tobacco smoke smell from your AC vents.

If you need help getting rid of any hazardous or harmless AC smells, please contact Aire Serv® today. We can answer any of your remaining questions and perform the necessary cleaning and repairs to make your home smell better when the air conditioner runs.