Why Mold Grows in a Dryer Vent
| Cause | What happens |
|---|---|
| Clogged vent | Wet air moves slowly and condenses on the lint |
| Sagging or overlong run | Water collects in the low spots |
| Run through a cold attic or crawl space | Warm exhaust cools and condenses inside the duct |
| Vent ends indoors or in the attic | Moisture and lint land inside the house |
The EPA's mold guide says to vent moisture-producing appliances, such as clothes dryers, to the outside, and to keep indoor humidity between 30 and 50 percent.
Signs of Mold or Moisture in the Vent
- A musty smell in the laundry room or on clean, dry clothes
- Water dripping from the vent hood or a damp spot on the ceiling below the run
- Clumped, wet lint at the outdoor hood
- Dark spots on the transition hose or around the wall opening
Musty air coming from the HVAC vents instead? The musty smell guide covers that system.
How to Fix a Moldy Dryer Vent
Clean the Full Run
Remove the lint and moisture from the dryer to the hood.
Replace Soft Hoses
Foil or vinyl hoses hold moisture and mold; Virginia code calls for a listed transition duct no longer than 8 feet.
Replace Moldy Sections
Duct sections with mold inside are cheaper to replace than to treat.
Fix the Route
Shorten long runs, remove sags and make sure the vent ends outdoors with a damper and no screen.
Run problems need dryer vent repair as well as cleaning.
How to Keep the Vent Dry
- Clean the lint screen with every load so air moves freely
- Keep the run short, straight and sloped toward the outside where possible
- Have the vent line cleaned when drying slows; the dryer vent cleaning page covers timing and cost
- Keep laundry room humidity between 30 and 50 percent