Why does mold grow in HVAC systems and attics?
Mold grows in HVAC systems and attics because they combine water, warmth and dust in places nobody looks. Central air conditioners pull water out of indoor air and send it through a drain pan and condensate line. Evaporative coolers do the opposite, adding water to the air. Attics trap heat and hold any water that gets in from the roof or the AC. When any of these leak, mold can grow for weeks before anyone notices.
AC closets and air handlers
Many East Valley homes have the air handler in a hallway closet, a garage or the attic. When the condensate line clogs, the drain pan fills and overflows. That water soaks the closet drywall, the floor or the ceiling below, and the closet is dark and enclosed, which suits mold. Rusted pans and missing or failed float switches are common in older systems.
Warning signs include water in the AC closet, staining on the closet walls, a musty smell when the system starts, and visible growth around the unit's base. Our guide to AC condensate line overflows explains how to keep the line clear.
Evaporative (swamp) coolers
Older homes in Mesa, Tempe and Scottsdale often still run evaporative coolers. Coolers work by passing air over wet pads, so they add humidity indoors. Problems start when:
- The cooler leaks onto the roof and into the ceiling around the duct
- The duct collects condensation and dust
- Pads and the water pan stay dirty and wet through the season
- The cooler runs during monsoon humidity, when indoor air is already damp
Attic mold
Attic mold usually follows a roof leak during monsoon season or an AC overflow from an attic air handler. Wet insulation sits against the ceiling drywall and stays damp in the heat. Bathroom fans that vent into the attic instead of outside add more moisture.
How we remove HVAC and attic mold
- Find and stop the water. We identify the leak, overflow or condensation source, and tell you which trade fixes it.
- Contain the area. Closets and attic sections are sealed off, and the HVAC system is shut down or isolated so it doesn't spread spores.
- Remove damaged materials. Moldy drywall, wet insulation and damaged ceiling sections come out.
- Clean the structure. Framing and roof decking are HEPA-vacuumed and cleaned.
- Dry to normal moisture levels.
- Coordinate HVAC work. A licensed HVAC contractor cleans the coil, replaces the pan or adds a float switch when needed.
- Rebuild drywall and insulation.
If the overflow is still wetting the ceiling, start with our ceiling and AC leak service so the structure dries first.