Black dust or streaks around your registers is usually “ghosting.” It happens when fine soot and dust particles are carried by airflow and deposited around vents, often where they meet the ceiling. Common sources are candles, cooking, fireplaces, poor filtration — and sometimes debris or mold inside the ducts themselves.
Common causes
- Soot from candles, cooking or a fireplace circulated by the HVAC system
- A low-quality or overdue air filter letting fine particles through
- Dust and debris inside the ducts being blown out at the registers
- Mold around vents in humid conditions (dark, sometimes fuzzy spots)
How to fix it
- Upgrade to a higher-quality pleated filter and replace it on schedule
- Burn fewer paraffin candles; improve kitchen ventilation
- Have your ducts professionally cleaned to remove circulating debris
- If spots are mold rather than soot, have them assessed and treated
When to call a pro
If the marks keep returning after you change filters and reduce soot sources, the buildup is likely inside your system. Professional air duct cleaning removes it at the source, and sanitizing helps with odors. If you suspect mold, see mold in air ducts. The U.S. EPA emphasizes source control as the most effective way to improve indoor air.
Frequently asked questions
Is black dust around vents mold?
Not always. Most black “ghosting” is soot and dust. Mold tends to look fuzzy or greenish-black and appears in humid areas — if in doubt, have it assessed.
Will cleaning my ducts stop the black marks?
If the source is debris inside the ducts, yes. If it’s candles or a poor filter, you’ll also need to address those to keep it from returning.
Seeing black marks at your vents?
We’ll find the source and clean it out — ask us for an inspection.