Why do ducts in South Florida get dirty and damp?
Warm, humid air is the main factor. A/C systems in Broward County run for much of the year, so the ducts move a lot of air. Moisture on cold duct surfaces mixes with dust, and that can leave a sticky film that holds even more dirt. Many older block homes have ducts in hot attics or garages, where flexible duct can sag, leak or pick up dust from the space around it.
Other common causes in Fort Lauderdale:
- Renovation dust from drywall, tile and sanding
- Salt air and fine sand close to the coast
- Pets, rugs and open windows between A/C cycles
- Leaky return ducts that pull in attic or garage air
If you notice a musty smell when the system starts, read our page on mold in air ducts. A smell does not always mean mold, but it deserves a proper look.

