Why Is My AC Spitting Water or Fog? (And Is It Dangerous?)

Turning on your air conditioner only to see a cloudy mist pouring from the louvers—or finding a puddle forming beneath the indoor wall unit—is understandably alarming. While smoke signals an electrical emergency, white fog and dripping water are usually tied to a breakdown in condensation management and humidity control.

​Why Is White Fog Coming Out of the AC Louvers?

​If the mist is odorless, disappears within seconds of touching the room air, and leaves no residue, it is not smoke. It is cold water vapor.

• ​Rapid Thermal Shock (High Humidity): When extremely cold air exits the coil and collides with warm, moisture-laden room air, the temperature drops below the dew point instantly. Moisture in the ambient air condenses into tiny visible water droplets, creating a temporary "cloud" effect.

• ​Dirty Evaporator Coils or Blocked Airflow: Restricted airflow forces the air moving across the coils to drop well below standard supply temperatures. When that superchilled air finally slips past the blockage, it fogs aggressively against ambient room air.

​Immediate Fix: Run the unit on a moderate fan speed for 10–15 minutes and close open windows or balcony doors to stabilize indoor humidity. If the mist smells metallic or burnt, shut the system off at the breaker immediately.

Why Is Water Leaking from the Indoor Unit?

​Your cooling system dehumidifies your space while lowering the temperature. As warm air hits the cold evaporator coil, water collects in a drain pan beneath the coil and exits through a gravity-fed or pump-assisted drainage pipe. When water leaks inside your living space, that pathway has failed.

• ​Clogged Condensate Drain Line: Algae, dust, and fungal sludge readily thrive in dark, moist drain lines. Once the line clogs, the internal drain pan fills and overflows down your interior wall.

• ​Disconnected or Cracked Drain Pan: Aging plastic pans can crack, or the drain hose fitting can work loose due to vibration over time.

• ​Improper Installation Pitch: Indoor units must maintain a slight, precise tilt toward the drain outlet. If shifted out of level, water bypasses the pipe entirely.

​Preventing Water Leaks and Fogging

1. ​Flush the drain line every six months with an approved anti-algal flush or vacuum extraction.

2. ​Wash mesh filters every two to three weeks during peak cooling seasons.

3. ​Inspect the indoor unit slope if you notice pooling at the non-drain end of the casing.

​Don’t let a minor drainage backup ruin your walls or flooring. Contact our certified HVAC service team to clear stubborn drain lines and check coil airflow today.