Why Is There Black Stuff Coming Out of My Air Conditioner Vents?

2017 Nov 28
Posted in: Air Conditioning

If you’ve noticed black stuff coming out of your A/C vents, it’s most likely either:

  1. Soot from candles or your fireplace (the most likely culprit)
  2. Mold spores
  3. Dark dust or dirty insulation

Let’s go into more detail about each of these problems and how you can fix them.

Need help right away? Give us a call, and we’ll quickly send over one of our trusted techs to fix whatever is causing the problem.

Problem #1: Soot from your candles or your fireplace

When a wax candle or wood in your fireplace burns, it produces tiny black soot particles.

And since your A/C system is constantly sucking in air from your home, cooling it, then blowing it back into your home, some of that soot inevitably gets pulled into your ductwork and pushed back out of your air vents.

So if you’re seeing black particles coming out of your air conditioner vents and you’re a fan of burning candles or your fireplace, the most likely culprit is soot.

Solution: Use a better air filter

The best way to prevent this black soot from circulating into your home is to upgrade to an air filter with a MERV of at least 13.

So what is “MERV” and what does it have to do with the soot particles flying out of your AC vents? Well, MERV (Minimum Efficiency Reporting Value) is basically a measuring system that determines how many particles and air contaminants a filter can catch. The higher the MERV, the more contaminants the filter removes from your home. 

You see, most homeowners use air filters with 8–10 MERV ratings, but these filters don’t catch smaller contaminants like smoke or soot particles. See the chart below for a side-by-side comparison of MERV 8 and 13:

merv 8 vs. merv 13 air filter
A MERV 13 filter can catch candle/tobacco smoke 

So here's the next step: Find your air filter and see what MERV you’re already using. You can usually see the MERV on the side of the air filter. If you’re not already using a MERV of at least 13, upgrade your filter to see if this gets rid of those pesky soot particles.

Not sure where your A/C filter is located? Or just want to know more info about why you’re seeing black soot? Read our related articles:

If you need help choosing an air filter, give us a call. We’d be happy to provide some recommendations.

Problem #2: Mold spores

Mold is a nasty fungus to have in your home. Breathing in mold spores causes harmful side effects like…

  • Throat irritation
  • Coughing
  • Wheezing
  • Eye irritation
  • Lunch infections

Unfortunately, it’s super common for mold to grow in or near your A/C system and ductwork. We’ll explain why. 

Mold needs 4 things to grow:

  1. Moisture
  2. Food (aka dust, debris)
  3. Warm temperature (80 degrees is best)
  4. Darkness (absence of UV light)

Now, your A/C system naturally has all 4 of these things: 

  1. Moisture (from humid air) 
  2. Dust (from dirty air) 
  3. Warm temperatures (because it’s located in an unconditioned space like your attic)
  4. No sunlight

That’s why it’s common for mold to form in or around your A/C system and ducts. And as air circulates through your system, it will pick up the mold spores in your ductwork and push them into your home through the air vents (which explains the black flakes around your vents).

Solution: Hire a mold remediation specialist

Mold spores look black and dark like this. If you see those black particles, you’ll need to have a mold remediation specialist…

  1. Confirm that the black particles are actually mold spores through a lab test
  2. Clean out your ductwork if it’s confirmed that you have mold growing inside

Problem #3: Dark dust is blowing into your home

Your home’s ductwork is located in unconditioned spaces like attics and behind walls, where all kinds of dust and dirty insulation abounds.


Leaky air ducts like the one pictured above allow dark dust to enter your home

Most homes have leaks or holes in their ducts, which means that dust and dirt can easily get sucked into the ductwork and blown into your home.

Solution: Have a professional clean and seal your ducts

To stop these black particles from entering your home, you’ll need a professional to…

  1. Seal your duct leaks using a mastic sealant or metal tape
  2. Replace any ducts that are beyond repair (if the holes or leaks are too severe)
  3. Thoroughly clean your ducts

For more information about duct cleaning and duct sealing, read these related articles:

Need a professional A/C repair in Arizona?

Just give us a call. We’d be happy to answer any questions you may have or help you schedule an appointment with one of our trusted techs.

Whether you need a duct repair or you need help choosing the right air filter we’ll help you get rid of those tiny black flakes.

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