Mold in Air Ducts? How to Get Rid of It?

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Mold in Air Ducts

Out of all the issues that can hit homeowners, mold is among the worst. It can cause a variety of health issues if left unchecked and is also hard to get rid of. When mold is visible, you can usually take care of the problem yourself, but the usual cleaning methods won’t work if the mold is in your air ducts. In this guide, we’re going to touch on the main causes of mold in air ducts and tell you how to get rid of it. 

What is Mold?

Most of us have experienced mold in some form, whether it’s on food left in the fridge or a damp area in a garage. Mold is a process of Mother Nature as it can help break down organic material, but when found indoors, it’s bad news for anyone living in your home.

Microscopic mold spores are able to float unseen through the air and deposit themselves on the surface of objects in your home. In warm, damp environments mold will multiply quickly, and central air conditioner systems are a prime target for this fungal growth.

Types of Air Duct Mold

Mold is a general term as there are over a dozen types of mold that can be found indoors. That makes the problem difficult to diagnose if you don’t know what to look for, so here’s a brief breakdown of the most common types of mold you’re likely to encounter.

Alternaria – You may not see this mold in your AC ducts, but it can certainly be found around your HVAC system. Alternaria is a greenish-brown with a velvety texture, which makes it easy to identify, and it’s typically found in areas that are consistently moist or wet.

Aspergillus – While it’s hard to mistake Alternaria, Aspergillus is the chameleon of the mold world. It can appear as white, green, or yellow, and there are 180 species of this fungus. It’s not as toxic as other molds on our list but can have adverse effects on the lungs of people with an underlying condition.

Acremonium – This white mold has a powdery appearance and a slow growth rate. It’s typically found around drain pains or coils but can also find its way into vents and air ducts. This toxic mold may take years to form and can be challenging to remove.

Chaetomium – If you see mold in your ductwork that looks like dirty brown cotton candy, there’s a strong chance it’s Chaetomium. It’s commonly found in water-damaged areas including vents that have a lot of condensation.

Fusarium –This mold doesn’t look like Chaetomium but is also caused by excess moisture and water-damaged walls.  It can also cause a variety of symptoms in humans, including onychomycosis, sinusitis, and disseminated infections in people with a compromised immune system. 

Stachybotrys – Stachybotrys, otherwise known as Black Mold, is another mold that’s easy to identify but hard to remove. This mycotoxin producing mold is toxic, and while it doesn’t typically take to metal, it can grow on dust and dirt in damp spaces.

Trichoderma – One of the more common molds found in vents and air ducts, Trichoderma thrives in wet areas. This multicolored mold can be tricky to identify but will spread rapidly through your vents once it finds a foothold.

Those are some of the most common molds found indoors, but even if you don’t see mold, it doesn’t mean it’s not present if the area stays damp or has an odor. If you’re suspicious of invisible mold, there are several affordable mold testing kits that can tell you if mold is present in your home.

The Effects of Indoor Mold

Mold can impact the health of anyone in your home in a variety of ways. Certain groups are more susceptible to these spores, however. The elderly and children are more prone to experience issues from indoor mold. It can also seriously impact people with asthma or conditions that affect their respiratory system. Some people in general are also more sensitive to mold than others.

One person may not experience any effects, while others could regularly experience headaches, itchy skin, or a stopped up nose. Coughing and wheezing aren’t uncommon, along with other upper respiratory tract issues brought on by mold exposure. There have been hundreds of studies on the health effects of indoor mold, and the overwhelming verdict is that you do not want it in your home.

How to Remove Mold from Air Ducts

Now that you understand a bit more about mold, it’s time to talk about removing it from your home. According to the EPA, if the moldy area is a patch around 10 square feet, you should be able to handle the problem yourself. For larger infestations, you will want to consider calling in a mold remediation company. We have some tips if you plan to call in a pro, but the steps below will help you remove small areas of mold around your HVAC system.

Personal Protection

Mold spores can cause a variety of respiratory problems but can also irritate your skin and eyes. Before you attempt to clean any mold, you need to ensure your lungs are protected. While you may have seen videos of people removing mold with dust masks over their faces, the best way to keep the spores out of your airways is with a respirator.

With the rise of Covid-19 around the globe, N-95 masks are something everyone has heard of. These masks can block particulates and cut down the risk of exposure to that virus, making them perfect for mold remediation. There are several variants of this mask to consider as well, although we only recommend one style.

K95 face masks with elastic straps are comfortable and ideal when you need to wear face protection for extended amounts of time. While expensive, a K-95 or P100 respirator like this model from 3M is designed for comfort and works with replaceable filter cartridges. These half-mask respirators provide a tighter seal, which makes them perfect for mold remediation.  

You don’t need to be nearly as picky with gloves but should choose long gloves that come at least halfway up your forearm. Rubber gloves will suffice with milder cleaning agents, but you will want to pick gloves made from nitrile or another chemical-resistant material for use with stronger cleaners. With your hands and mouth covered, the last area we want to fully protect is your eyes.

Safety goggles are something you may have lying around the garage, but a traditional pair isn’t suited for microscopic mold spores. When you need a tight seal with an anti-fog lens, you can’t go wrong with the DeWalt DPG82-11C safety goggles. They are affordable, comfortable, and sport a built-in ventilation channel.

While you won’t crawl through air ducts, mold can get onto your clothing and be carried indoors. Depending on how severe the issue is and where it’s located, you may want to consider a Tyvek suit as well. It’s what a professional mold remediator wears when working in basements and something that will keep your clothes mold-free as well.

Cleaning Supplies

All of the items above will keep mold out of your airways and eyeballs, but you still need to pick up a few cleaning supplies. Unless you have extremely thick trash bags in your home, you’ll want to pick up thick contractor garbage bags around 6 mils thick. Plastic scrapers are an inexpensive way to remove mold from flat metal surfaces, although you’ll want to use a wire brush if any wood near your venting has been contaminated.

When it comes to cleaners, there is no shortage of options to choose from. You can find non-abrasive mold cleaners alongside jugs of concentrate and antibacterial solutions. One of the first we want to recommend is Concrobium Mold Control. It’s EPA-registered, easy to use, and comes in a concentrated solution or 32-ounces spray bottle.

Mold Armor has a similar product that works as an HVAC mold cleaner and can eliminate 99.9% of household bacteria in less than a minute. Both products can be used to loosen and remove light mold in or around air vents. When you need something stronger, we highly recommend Shockwave RTU from Fiberlock. It’s a professional-grade product that’s EPA-certified and outstanding when it comes to mold and mildew removal.

Removing Mold from Air Ducts

Keep in mind, this process is only suitable for small areas with mold problems, not your entire system. If you believe mold has spread throughout your air ducts, the best thing you can do is save yourself a lot of time and money by bringing in a professional.

If you plan on cleaning the mold yourself, you need to turn off your air conditioning system, put on your protective gear, and carefully follow the directions on the cleaning product. Each company will have its own recommendation or process, and there’s no universal solution given the range of vents found in homes today.

When your solution is ready, you simply need to scrub the area until the mold is removed. It may take more than one application, but when you are done, dispose of rags, brushes, or scrapers in an airtight construction bag. When satisfied, the next step should be to use a mold inhibitor in the area to ensure it doesn’t return.

This video shows what you can expect when cleaning an overhead vent and how they addressed the cause behind dust, mold, and dirt around the vent.

Professional Help

When the vents in your house are moldy, there’s a chance the ductwork could have mold growing inside as well. Unfortunately, it’s difficult to diagnose without the right equipment, which is why it’s wise to call in a professional.

The methods of removing mold from large areas like basements and crawl spaces can vary from Dry-ice blasting to manual scrubbing, but things are different with ductwork. These tight spaces can be time-consuming to clean, which means the cost of mold remediation can be high.

If you plan on hiring a company to clean your AC unit or ductwork, make sure they will deal with mold. Some companies also only service units and don’t actually clean ductwork or vents at all. When vetting a mold remediator, ask about their process, check for proper credentials, and make sure they guarantee their work.

Preventing Mold in Air Ducts

The best way to fight mold growth in your home or air ducts is to remove its food source. Without water and material to munch on like dust or old wood, mold doesn’t have a place to grow. With that in mind, here are some preventative tips to keep mold from growing in your air vents or ductwork.

If you have a basement and can see water dripping from your ductwork during the summer, a dehumidifier can help bring the humidity levels back in the normal range. It’s something 90% of mold remediators recommend for basements that stay damp, whether it’s from Mother Nature or leaking air ducts.

On that note, leaks in your ductwork can result in excess moisture and mold. Sealing leaks around vents is an easy DIY project and one that will save you from some headaches down the line. Anything that can cause a drastic temperature differential can potentially leak to mold. That includes oversized AC units and areas with poor ventilation.

Ultraviolet rays are a great way to combat germs and bacteria as they can break down the bonds that hold those particles together. It’s a common feature on air purifiers, but you can also install a UV-C light on your HVAC system or in the ductwork. These systems are simple to install and can significantly impact your air quality, but you still need to have any mold removed beforehand.


As you can see, mold can be challenging to remove compared to ordinary dirt and grime that’s normally found in air ducts and vents. Unless you have light mold on your vents, we recommend consulting a professional that can properly clean your vents to ensure no mold remains hidden in the ductwork. If your ducts are just dirty and not moldy, this guide will help you get them clean in no time.


Q: Can mold grow in cold weather?

A: Despite what many people believe, mold can still grow in cold weather. While it can spread rapidly at temperatures above 60°F, it can even grow in uninsulated areas with a large temperature differential.

Q: Will bleach work to kill mold?

A: You can remove mold from surfaces with a solution of 1 cup bleach to a gallon of water, but bleach can cause discoloration on some metal surfaces.

Q: What’s the best humidity level to prevent mold growth?

A: The optimum temperature range is between 30% to 50% if you want to prevent mold from growing in your home.

Q: Can I use a HEPA vacuum for mold?

A: HEPA vacuums are something most professional mold services use. Given their price and the process of completely cleaning mold, it’s usually not a cost-effective solution for homeowners.

Q: Is it possible to make mold worse by attempting to clean it?

A: Yes. It may not be an issue with smaller spots, but you can send mold spores flying through your ductwork and into other parts of your home if you don’t clean carefully. 

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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