Types and Signs of Mold in Air Ducts

Mold requires a warm, moist environment to thrive. Humidity, moisture, poor ventilation, and materials such as dust, debris, and dirt all contribute to the ideal setting for mold to thrive and grow in air ducts. Lack of proper cleaning and poor maintenance can also encourage mold to grow and spread in your home environment. Below is a discussion of the types of mold in air ducts and signs you may be dealing with a mold problem 

Types of Mold in Air Ducts

The following are some of the most common types of mold found in air ducts.


Acremonium is a toxigenic mold that looks like a powdery, white substance. This mold is likely to be concentrated in the moist and wet parts of your air ducts and may form for months or years before you recognize a problem. 

This type of mold rarely infects human beings. However, acremonium may grow together with other types of mold and cause health issues such as pneumonia, endocarditis, and subcutaneous infections in humans.


Aspergillus can be difficult to identify if you have an untrained eye, as this aspergillus mold takes on different appearances. You will spot this mold as a white, brown, or yellow mold commonly found around areas with leaks. 

This mold type threatens human health and can cause symptoms such as shortness of breath, fever, chills, and joint pain.


Fusarium will likely spread beyond the air ducts and onto surfaces that are prone to condensation. You will likely experience this mold if your air ducts suffer from issues such as water leaks and condensation. 

This mold type appears white, brown, or yellow and can take on a variety of textures and consistencies. Thankfully, this fusarium is relatively harmless to humans, except for those who are immunocompromised.


Mucor is a highly toxic mold that grows in the air conditioner unit and quickly spreads through the duct system. You must deal with mucor as soon as possible to prevent adverse health effects in your household.


You can easily identify Stachybotrys by its characteristic black color. However, you may need help to spot this mold type as it thrives deep in air ducts with adequate moisture.

Strachybotrys is toxic and can cause nasal irritation, dyspnea, chest tightness, wheezing, and coughing. Some people also report mental fatigue and lightheadedness.


Trichoderma can either be greenish, greyish, or whitish. This mold type needs a steady water supply in the duct system to thrive. Your air conditioning system allows the growth and spread of this strain to the duct system.

Signs You Have Mold in Your Air Ducts

Some signs that you have mold in your air ducts include the following.

Black Dust

If you notice black dust that is hard to wipe off, especially around air conditioning vents, you may have a black mold problem. This mold type is toxic, so you must contact a professional to help clear it as soon as possible.

Medical Symptoms

Another way to recognize mold growth in your home is to look for the physical signs. Itchy eyes, lightheadedness, headaches, nausea, dizziness, and fatigue when you turn on the air conditioner are some signs that you may have mold in your air ducts.

Musty Smell

Black mold has a distinctive musty smell. While this odor may go unnoticed initially, you eventually realize a persistent, unpleasant smell and worsening health symptoms.

You should contact a qualified HVAC professional as soon as possible if you suspect that your air conditioner may be affected by mold. American Air Heating & Air Conditioning is a qualified Northern Colorado-based HVAC contractor with extensive experience dealing with mold in homes. Contact us today for mold removal.