Aspergillus and Cladosporium are among the most commonly found mould genera in residential AC ductwork, thriving in the dark, occasionally damp conditions inside a duct system, though exact identification requires lab testing rather than visual assessment alone.
Why Ducts Are a Favourable Environment
Ductwork combines low light, occasional condensation-driven moisture, and a steady supply of organic dust for mould to feed on, which together make it a more hospitable environment for mould growth than most exposed indoor surfaces. Once established, mould inside ducts is distributed through every room the system serves.
Common Genera Found in HVAC Systems
Aspergillus and Cladosporium are frequently identified in HVAC-related mould sampling due to their tolerance of the conditions inside ductwork, though Penicillium and Stachybotrys (commonly called black mould) can also occur where moisture problems are more severe. Visual colour alone isn't a reliable way to identify the species present.
What This Means Practically
Regardless of the specific type, mould inside ducts should be treated the same way: removed through professional cleaning and, where growth has been significant, followed by a sanitisation treatment rather than assumed to be harmless because it looks minor. Persistent musty odour is often the first noticeable sign before any mould is visually confirmed.
If this sounds like what's happening with your unit, our AC Duct Cleaning page covers exactly how we handle it, or you can message us directly for a same-day assessment.
Frequently Asked Questions
Do I need lab testing to know what mould is in my ducts?
For most residential situations, professional cleaning and sanitisation address the problem regardless of species; lab testing is more relevant for unusual health complaints or legal/insurance situations.
Is black mould in AC ducts dangerous?
Stachybotrys and other mould types can trigger allergic or respiratory symptoms in sensitive individuals; any confirmed or suspected mould in ductwork is worth addressing rather than ignoring.
Can mould in ducts come back after cleaning?
Yes, if the underlying moisture source, such as a condensate leak or high indoor humidity, isn't also addressed alongside the cleaning.