Why Is My Window AC Leaking Water Inside the House?

1. Improper Installation Angle

Window air conditioners are designed to pull humidity from the indoor air. This moisture condenses into water and drips into a drain pan. If the unit is perfectly level or tilted slightly forward into the room, that water will spill inside. Fix: Reposition the AC unit so it has a slight downward tilt (about 1 inch) toward the outside. This allows gravity to pull water out the back drain.

2. Clogged Drain Hole

Outside dirt, leaves, and debris can easily clog the small drain hole at the back of the unit. When the pan overflows, the water has nowhere to go but inside your home. Fix: Locate the drain hole on the back or bottom rear of the unit. Use a wire or an old toothbrush to clear the blockage.

3. Blocked Condensation Pan

Over time, algae or mold can grow inside the internal drain pan, creating a blockage before the water even reaches the exterior drain. Fix: You'll need to remove the front grill and clean the drain pan using a mixture of white vinegar and water.

4. Frozen Evaporator Coils

If the coils freeze (usually due to a dirty filter), the ice will eventually melt. If it melts too quickly when the unit is turned off, the drain pan can overflow and spill inside. Fix: Check and replace a dirty filter. Let the ice melt completely, then turn the unit back on.

5. Cracks in the Drain Pan

Older units can develop cracks in the plastic or metal drain pan. If this happens, water will leak regardless of the tilt. Fix: A cracked pan often means it's time to replace the unit, as replacing the internal pan is highly labor-intensive.