Table of Contents
- What is the black stuff coming out of AC vents?
- Causes of black dust around air vents
- How to Get Rid of Black Dust Around Air Vents
Air vents ought to be clean for the air in your house to be pure and safe. But when you see black dust settling around air vents, something is definitely wrong. What could be the cause and how can you get rid of the black particles from the air ducts?
Black dust around air vents can be mold, soot, or dust that combines with moisture to form moldy stuff on air conditioner vents. To remove the black dust, wipe the air vents with a piece of cloth soaked in a vinegar solution and then reduce the dust and humidity in your house.
What is the black stuff coming out of AC vents?
Your AC unit produces moisture which can condense and settle around the air ducts and air vents of the machine. Dust settles on all surfaces, including the air conditioner vents that are moist, forming a conducive medium for mold to grow and form black stuff around air vents.
Therefore, the black stuff coming out and forming around AC vents is most likely black mold, but it can also be soot (smoke) or dark particles of dust from outside your house.
Causes of black dust around air vents
If you have central heating, ventilation ducts, and air conditioning (HVAC) system installed in your home, you’ll likely notice black dust settling around your air supply and return openings especially if you don’t clean these air vents and outlets on a regular basis.
Here are the possible causes of black dust surrounding air vents:
Mold fungi species find the parts of a HVAC system as a conducive habitat as it provides the conditions necessary for the spores to germinate and thrive.
For instance, mold thrives in moisture, which is always present in the humid air that your HVAC system sucks in through the vents, grilles, and other types of AC openings.
Mold also needs dust to survive as it feeds on the dead cells within the dust build-up. This dust is usually present in vents as dirty air from adjacent rooms passes through the air vents into the HVAC ducts.
Also, since direct UV light inhibits the growth of mold, the interior location of HVAC systems- where there’s no direct exposure to UV light- makes them a perfect habitat for mold. The mold spores are then usually pushed from the internal ductwork and out onto the vents, grilles, and registers as the HVAC system circulates fresh air back out into the rooms.
Mold spores are typically black and dark in color, which is why you’ll start noticing black flakes around your air supply openings.
Pro tip: Ensure you place your HVAC unit where there’s no air obstruction. Putting things that block the free flow of air to and from heating and cooling systems in the house makes it easy for mold to grow on surfaces in your house.
Soot from candles and fireplace smoke
Soot from the fireplace or burning candles in the house for dehumidification is arguably the most common cause of black dust on AC vents.
As you burn wood or candles in your fireplace, they release tiny soot particles that are then inadvertently sucked into the air conditioning system via the AC vents, registers, and grilles. Over time, the black soot particles will build-up within your vents and will bear a noticeably dark color.
Even a gas fireplace can produce soot if the burner ports are clogged causing incomplete combustion of gas. Any small amount of such soot in the house can easily settle around the cool air vents of your AC unit, causing the black stuff. If you do not clean the black stuff regularly, some AC units will stop cooling the house due to clogging.
Dark dust leaking into the house
Your HVAC’s duct-work typically passes through unconditioned sections of the house such as within the attic, through the ceiling, and behind drywall.
Should an air duct start leaking due to irregular maintenance, it’ll pick up dark dust particles that have built-up within these spaces. The dust then gets sucked outwards into your vents.
If you don’t have a good HEPA air purifier that can get rid of fine dust particles in your house, you can easily find small dust particles escaping into your house from leaky ducts and into your house. The dust particles settle on different surfaces, including air vents.
Even dust mites can also settle on these surfaces, according to a study published in the International Journal of Clinical and Experimental Medicine – “The study concludes that air-conditioner filters can enrich dust mites major group allergen, and the allergens can induce asthma. The air-conditioner filters shall be cleaned or replaced regularly to prevent or reduce the accumulation of the dust mites and its allergens.”
How to Get Rid of Black Dust Around Air Vents
The first thing you want to do is to take a closer look at the black flakes around your air vents and grilles to determine that they’re indeed mold spores. Once you’re sure, you first want to make sure you wear surgical face mask to safeguard yourself against potential health issues that might be triggered by inhaling mold spores.
To get rid of black dust around air vents, detach the covers that have the mold and soak them in a bucket full of water mixed with detergent. Clean them for 20 minutes and then wipe with a cloth soaked in a vinegar solution to kill off all the mold and prevent new growth. Refit the AC covers.
Here’s the complete procedure to clean and remove black dust on AC vents elaborated:
1. Remove the AC covers that have black dust
Remove the mold-infested covers of the AC openings- whether it’s an HVAC vent, grille, register, or a diffuser. Remove its cover by unscrewing it from the wall, ceiling, or floor. You might want to dust them off before vacuuming the whole room to help control the dust.
2. Soak the moldy vents in water with detergent
Place the vent covers in a large bucket and fill the bucket up with water until the vent covers are wholly submerged. Then, add some detergent and let the vent covers with mold soak in the solution for about 20-minutes.
3. Air-dry the vent covers and clean your AC’s interior
Once the 20-minute wait-period elapses, let the vent or grille covers air-dry. Meanwhile, proceed to clean up the interior of your AC system where the mold spores may be coming from.
To effectively do this, spray water onto the AC blades and the openings of the air ducts. After water-spraying the duct openings, wipe them with soapy water to ensure that all mold spores are eliminated.
4. Wipe AC ducts and vents with bleach
Now, mix a cupful of bleach with a gallon of water in a large bucket and use the bleach solution to wipe the duct openings, blades, and the inner parts of the vent openings. If you’re venting your portable air conditioner with window ducts, remove them and clean them thoroughly before refitting them back.
5. Refit the vent covers afresh
Once the inner parts of the vents that you had bleach-washed have dried up, replace the vent covers that you’d cleaned-up earlier and left to air-dry.
Finish off by properly discarding the dirty water and solutions which you’ve used to kill mold on your various air-vent components.
NB: For elimination of black dust on air vents caused by soot and dark dust from ductwork leaks, you can adopt steps (2) to (5) above, after which you can proceed to undertake preventative measures to prevent the same from happening in the future, as detailed in the next section.
To prevent soot from causing black dust on your HVAC system’s air outlets and inlets, replace your current air filter with a premium-quality alternative that boasts a MERV RATING of 13 or higher. MERV is an acronym for the Minimum Efficiency Reporting Value, which is a measure of a filter’s capability to trap/capture air contaminants- including dust particles.
Meanwhile, to prevent black dust being caused by dark dust being blown into the AC system from unconditioned spaces within the house, ensure to seal up any leaking HVAC air ducts that are letting in the dust.
A professional HVAC maintenance guy will typically use metal tape to seal up leaking ducts, or fully replace ducts that have been damaged beyond repair.
Keep in mind that when black stuff builds-up on AC vents and other air outlets in your home, it can be dangerous to your health in many ways. Eye and throat irritation, persistent sneezing, and breathing problems can result from the black dust. It’s important to identify the causes of the dark dust and get rid of it in order to improve air quality and make your home clean and healthy.
- The United States Environmental Protection Agency (EPA): Heating, Ventilation and Air-Conditioning Systems, Part of Indoor Air Quality Design Tools for Schools
- Wanda Eubank and Betty Feather, University of Missouri Extension: How to Prevent and Remove Mildew — Home Methods
- Xiaodong Zhan, The International Journal of Clinical and Experimental Medicine: Air-conditioner filters enriching dust mites allergen
- University of Virginia Housing and Residence Life: Mold Prevention
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.