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Mold Growing Inside Air Ducts
in Sioux Falls, SD
Mold inside ductwork is a real problem, and it spreads fast once it starts. Sioux Falls summers push humidity levels high enough that any cool duct surface can sweat, and that standing moisture is all mold needs to get going. If you ignore it, the system blows spores into every room every time it runs.
Quick Answer
Mold grows inside air ducts when moisture gets into the system and has somewhere dark and still to sit. In Sioux Falls, humid summers combined with cold duct surfaces create condensation that feeds mold growth. The fix involves cleaning out the mold and finding where the moisture is coming from. Call (605) 250-4261 if you smell something musty when the AC or heat turns on.
Telltale Signs
Warning Signs to Watch For
- Musty or moldy smell that gets stronger when the HVAC system turns on
- Black, green, or white spots visible on or near vent covers
- Family members have more allergy or sinus symptoms indoors than outside
- You see moisture or condensation on duct surfaces in the basement
- A visible dark film inside the duct when you pull off a register
Root Causes
What Causes Mold Growing Inside Air Ducts?
Condensation on Cold Duct Surfaces
When warm humid air from a Sioux Falls summer hits a cold metal duct surface, water condenses on the inside wall. That moisture sits in the dark duct interior and mold starts growing within 24 to 48 hours if it doesn't dry out.
The Fix
Duct Cleaning and Moisture Control
Technicians remove the mold growth and treat the duct interior, then address the condensation issue by checking insulation on the ducts. Keeping the duct surface from getting so cold reduces future condensation.
Oversized Air Conditioning Unit
An AC unit that is too big for the house cools the air fast and shuts off before it runs long enough to pull humidity out of the air. The result is cool but damp air sitting in the ducts, which is exactly the condition mold needs.
The Fix
Duct Cleaning and HVAC Sizing Review
Clean out existing mold first. Then have the AC equipment reviewed by an HVAC tech to see if the unit size is right for the house. A properly sized unit runs longer and keeps humidity lower.
Water Intrusion Near Duct Runs
In Sioux Falls homes with basement or crawl space duct runs, a wet basement or a foundation crack lets water in near the ductwork. That moisture raises the humidity around the ducts and can get inside if any seams are open.
The Fix
Duct Cleaning and Source Waterproofing
The ducts need to be cleaned and dried out, but fixing the water entry point is what actually solves the problem. Cleaning ducts without stopping the moisture source just means the mold comes back.
Self-Diagnosis
Which Cause Applies to You?
Check the signs you're observing to narrow down the likely root cause before your inspection.
| What You're Seeing | Condensation on Cold Duct Surfaces | Oversized Air Conditioning Unit | Water Intrusion Near Duct Runs |
|---|---|---|---|
| Musty smell only when the HVAC system is running | |||
| Condensation visible on duct surfaces in summer | |||
| AC cycles on and off frequently and house still feels humid | |||
| Water stains or dampness visible on basement floor near duct runs | |||
| Dark spots visible inside the duct opening when register is removed |
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