Mold in Air Ducts Symptoms

The bad news is that your air ducts can become home to different kinds of mold. Unfortunately, some strains can cause a wide range of health problems, starting from itchy eyes and throat and ending with more serious respiratory issues. Moisture, a musty smell, and black dust can also become symptoms of mold in air ducts.

How can you remove this nasty thing from your HVAC system? What are the most common types of mold that you should be aware of and, finally, how can you prevent mold from growing in your ducts? 

Below is everything that you need to know. 

Also see: Why there is a bad smell coming from one vent in the house?

Signs of Mold in Your Air Ducts

How can you tell that there is mold in your HVAC system? Thankfully, some of the signs are relatively easy to spot.

Visible Mold

The most straightforward sign is, of course, actual mold. If you see fuzzy white fibers (that remind you of cotton balls) or a stain that looks suspicious – it looks like you are dealing with mold.


Moisture is the thing that causes mold growth in the first place, but did you know that if your AC has this substance inside, it is going to create added moisture inside the house? 

Firstly, such indoor moisture is extremely unpleasant. Secondly, and most importantly, such conditions encourage further growth of mold and various bacteria.


One of the most obvious signs of mold in your HVAC system is an unpleasant, musty smell. The smell reminds some people of dirty socks or feet. In any case, a bad odor is definitely an indicator that something is wrong with your unit.

Black Dust

You might notice strange black dust around the vents. This means that there is black mold growing inside.

The main difference between black dust and simple dust is that it is quite challenging to wipe black dust off.

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Itchy Eyes

The most dangerous thing about mold is that it can affect the health of everyone who lives in the house. If your family members or friends started suffering from various health issues, problems with your HVAC system might be to blame.

You should look out for allergy-like symptoms. Itchy eyes can be an indicator of mold in your air vents.

Itchy Throat/Difficulty Breathing

Continuing with the physical symptoms – mold in the unit can result in an itchy throat. The members of the household might also experience difficulties when breathing.


Do you feel different, once your AC gets turned on? You might start feeling nauseous, get headaches, unexplainable fatigue, or even dizziness. All these symptoms indicate that there is already quite a lot of mold growing in the system and you have to try to take care of the problem as soon as possible.  

Some other physical symptoms include a runny nose, itching skin, headaches, coughing, sneezing, neurological issues, and tightness in the chest.

According to the National Academy of Science, 15-50% of people who are genetically prone to allergies are allergic to mold. They will, most likely, develop the symptoms that we have mentioned above. 

Also see: How to prevent mold in window AC?

Most Common Types of Mold in Air Ducts

The more you know about your enemy, the easier it is to eliminate the rival, right? 

  • Alternaria

This type looks like it has a velvety structure. It is usually green or brown and is extremely widespread. 

  • Fusarium

This type of mold is known for spreading outside of the ducts and starting to grow on your walls and other surfaces that receive condensation.

  • Acremonium

It takes at least a few months for this mold to form. It has a white color and looks powdery.

  • Mucor

Mucor is very toxic and can easily spread throughout the whole HVAC system. It is greyish or white in color and usually grows in patches.

  • Aspergillus

It is quite challenging to identify this type, as it comes in various forms and colors. However, in most cases, it is yellow, white, or brown.

  • Trichoderma

A pervasive form of mold that is first transparent in color, but then becomes white and yellow. After that, Trichoderma darkens and begins producing spores. 

Fun fact: some Trichoderma smell like coconut.

  • Stachybotrys

Possibly, the worst out of them all – Stachybotrys or black mold. This type in general doesn’t really like to grow on metal air ducts, it prefers wet drywall. In any case, it is a very toxic substance that grows quickly and, usually, deep in the system.

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How to Remove Mold from Your Air Ducts

If you have noticed any of the symptoms mentioned above, then you should act immediately. Otherwise, the mold will have more time to grow deeper into the HVAC system and affect the health of everyone living in the house.

The most effective solution is to call a team of professionals. Ideally, the experts will be able to deal not only with the actual mold but also with the thing that is causing it to grow.

However, there are also a few DIY solutions that you might want to try out.

Do bear in mind that scrubbing mold with regular cleaners will not make it go away. There will be just enough left behind for it to grow back. Also, do remember that you can accidentally damage the unit if you attempt to clean the HVAC system on your own.

Related post: Duct cleaning after renovation. Do I need it?

A Step-by-Step Guide to Removing Mold

  • Choose your fighter. It can be a commercial mold removal (go for an EPA-approved solution), a mixture of 1 part of bleach and 16 parts of water (works on various non-porous substances), or a mix of a tablespoon of home detergent, half tablespoon of baking soda, and a cup of water.
  • Make sure to protect yourself both from the mold and your chemical of choice. Use safety goggles, thick gloves, and a mask.
  • Turn off the vents.
  • If you are able to reach the affected spot, then start scrubbing the area with a brush or a wet rag.
  • Do use airtight garbage bags when getting rid of the rags used.
  • Apply mold growth inhibitors. Unfortunately, without this chemical, the mold will, most likely, come back.

You can attempt removing the substance on your own, only if you know that a small area has been affected. In case your bathroom smells musty, you can try tackling only the vent that aerates this particular space.

Don’t forget that even if you manage to effectively remove the intruder from the visible area, it can still be present in the actual HVAC system in the form of mold or spores. 

How to Prevent Mold from Growing in Your Air Ducts

Mold is stubborn. And it likes to come back from time to time.

Taking into consideration the health risks and the damages that mold can do to your house and the HVAC system, you should try to not only remove the annoying substance but also do everything you can to prevent it from occurring in the first place (or coming back).

  • Control humidity levels. You should attempt to keep the humidity levels between 30% and 50% all the time. Mold needs moisture, in order to develop. In fact, it needs as little as 2 days to grow, once a specific area has been affected by moisture (including water leaks).
    You might want to consider getting a dehumidifier.

Related Post: What will absorb moisture in a room?

  • Try to immediately fix leaky windows, pipes, or roofs.
  • Make sure that your house has enough ventilation. Pay extra attention to your bathroom, the laundry room, and the kitchen. You can use exhaust fans that vent outside the house.
  • Don’t use carpets in areas that can have a lot of moisture (like bathrooms, and basements).
  • When it comes to the actual HVAC system, you should replace the filters, insulate the air ducts to reduce condensation, clean the drip pans on a regular basis, and do your best to try and keep the whole system dry.
  • You might want to consider getting your ducts professionally cleaned everyonce in a while, especially, if you live in a humid area.
  • Ionization air purifiers and UV light might be able to kill mold and other nasty things, so installing one of these things or both might be a good decision. 

To Sum Up

Now you know everything about mold in air ducts symptoms.

If you have noticed that…

  • There is mold around the ducts
  • Your house has a strange, musky smell
  • The humidity levels in the house have risen
  • There is black dust around the vents
  • The people that live in the house started suffering from allergic reactions and various respiratory problems

…then you might have mold growing in the HVAC system.

There are quite a few types of this substance that can make your ductwork their home. Unfortunately, all of them pose health risks, so getting rid of mold should become one of your top priorities. 

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You can attempt to remove the mold on your own, but getting help from a team of professionals might be more effective.

What you can do is try to prevent the mold from coming back by following a few simple tips that we have mentioned.