Said It Here

Black buildup around air vents: mold or dust?

Dark buildup around vents is often a combination of mold and accumulated dust and dirt rather than just one or the other. Homeowners find themselves unsure of what the stains actually are, leaving them questioning whether they are dealing with mold or simply filthy vents.

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

  1. 1
    Replacing metal vents with plastic ones to reduce condensation caused by warm air touching cold metal.
  2. 2
    Keeping the air conditioning turned off to avoid blowing grime into the room
  3. 3
    Trying to manually wipe inside the vent as far as possible

In their words

Unedited, most upvoted first, each linked to the thread it came from.

“We noticed stains outside the vents, so I took them down to check. Is this mold or were they just filthy?”source ↗

Tizz986 · r/hvacadvice · 1 upvotes

“Mold. Dust usually costs pretty evenly. Mold starts out more spotty.”source ↗

Soulful_Panda · r/hvacadvice · 1 upvotes

“Not an expert but looks like some mold”source ↗

GardenOrca · r/hvacadvice · 1 upvotes

“Mold AND dust/dirt”source ↗

Ancient_Substance152 · r/hvacadvice · 1 upvotes

“Three weeks ago, a patch of black particles appeared on my bedding.”source ↗

“Now I'm afraid to turn on the a/c for fear of blowing this black grime into the air.”source ↗

“I'm at my wit's end, not being able to turn the a/c on for 3 weeks in scorching heat.”source ↗

Consistent-Box6864 · r/hvacadvice

Where this came up

r/hvacadvicehome maintenancehvachvac maintenanceindoor air qualitylandlord tenant issuesmold

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