Why Does the Air From My Vents Smell Musty From the Air Conditioner?

Air conditioners cool air while reducing humidity indoors. If you experience a musty or moldy smell coming from your vents, then there is likely mold somewhere within the heating and cooling system of your home.

Air conditioners can create musty smells in your home.

You may be able to remedy some mold problems yourself, whereas a professional may have to treat large and involved mold issues.


Air conditioner size can cause a musty smell indoors. If the air conditioner that cools your home is sized too large for the size of the home, it results in the unit being unable to remove the moisture from the air. When moisture remains in the inside air, mold spores can grow and cause a musty smell. If your air conditioner is too large, contact a professional to determine if you need to install a smaller size air conditioner.


Your air conditioner may be leaking water that can host mold, which will result in a musty smell in your home. Air conditioners drain water through drainage systems and drip trays. If these systems in your air conditioner are ineffective or leaking, the resulting stagnant water can house mold. Clean any stagnant water and repair leaking or broken drains and drip trays. Thoroughly dry the area with a fan to remove any remaining moisture.

Ducts and Vents

Some homes may have mold growing within the ducts and vents of the home. Mold growth is caused by excessive moisture in the air. When the heating and air conditioning system is in use, a musty smell will escape from the vents due to the mold. Some mold may be seen with the naked eye, or it may be hidden deep within the vents. A duct cleaning company can inspect a duct system for mold and clean the ducts and vents for a fee. If mold persists or is unable to be cleaned, you should replace the ducts or vents.

Improper Use

If an air conditioner is improperly used, it may result in mold and musty smells. Air conditioner manufacturer Panasonic suggests that running an air conditioning unit in economy mode may be ineffective at removing humidity, which can result in mold growth and musty smells. Panasonic suggests running a unit in fan-only mode to help with evaporating any moisture that has built up within the unit and vent system.


To remedy the musty smell, you must determine where the mold is located and completely remove it. An air conditioning professional can assess the performance of your air conditioner to ensure that there are no leaks or breaks causing a mold problem. Duct cleaning companies can determine if mold is present within the ducts of your home and can clean them to remove mold. To reduce humidity within your home, check for leaks and moisture and ensure that windows, doors and walls are properly sealed and air tight.