10/06/2026
https://loom.ly/4x9ej_E
You notice a dark gray or black stain around an air vent. Your first thought: Is that mold?
Maybe—but not necessarily.
Dark staining around HVAC vents can be caused by ordinary household dust, air leaks around the register, soot from candles or fireplaces, cooking residue, moisture issues, or other airborne contaminants. And if you clean it off only to have it come back, your home may be telling you something worth investigating.
Before you assume the worst—or simply paint over it—find out what could be causing those dark marks and what they may tell you about your HVAC system.
Need help understanding what’s happening inside your system?
Visit mrductcleaner.com or call 844-444-DUCT for a Free Estimate.
Noticed black stuff around your air vents? Learn what causes dark HVAC vent stains, when moisture may be involved, and what you should check next.