When the outside air is hot and humid, you rely on your air conditioning system to keep you cool and comfortable. Therefore, a foul odor wafting through your living space can be startling. If the stench isn’t coming from your trash or a pet accident, it might be emanating from your AC unit. Use this guide to get to the bottom of that smell.

4 Common HVAC Smells & Their Causes

1. Gas

If your home is connected to a natural gas line, it’s possible that this chemical is leaking out of your HVAC system. If so, you’ll notice a rotten egg-like odor coming from the vent. Since gas is flammable, turn off the unit and evacuate your home before calling your gas provider.

2. Musty

ac unitAC units are excellent at controlling indoor air humidity, and as a result, they may gather condensation. If this moisture isn’t escaping properly, it may sit inside the unit or its ducts, leading to mold or mildew growth, which creates a musty smell.

3. Burning

This smell could indicate a mechanical issue, such as a broken fan or belt. These broken parts cause the system to overheat. To prevent a fire, turn your HVAC unit off as soon as you notice a smokey odor.

4. Rotting

This scent usually indicates that a small animal, such as a rat or bird, got trapped into the ductwork. The foul smell is emanating from their decomposing body, and if you have a central air conditioning system, the odor will be distributed throughout the home.


If you encounter any of these smells in your home, contact the knowledgeable team at Cool It Kauai Air Conditioning in Kapaa, HI. Since 2018, these professionals have provided residents and businesses with AC unit installation, maintenance, and repair. Owner Van Skoubis has over 10 years of industry experience and is on-site at every job. Call (808) 315-1888 to schedule an appointment, or connect with the team on Facebook to receive the latest news and updates.