My Window AC Unit Is Leaking Into the Wall, What Happens Next?

Water leaking into a wall cavity does not dry on its own. The insulation and wood framing remain damp, creating a perfect environment for mold growth. Mold can begin to develop within one to two days in a humid climate.

Structural damage is another major concern. Prolonged moisture weakens wall studs and drywall, potentially leading to costly repairs. The humid continental climate with cold winters and hot humid summers, like in Staten Island, can accelerate these problems.

• Mold spores thrive on damp drywall paper and wood.
• Wet insulation loses its thermal resistance (R-value).
• Metal fasteners and electrical boxes can corrode.
• Wood rot compromises the wall's strength over time.
• Hidden moisture can warp flooring and baseboards.
• Musty odors often indicate microbial growth inside.

A blocked condensate drain line is the most frequent culprit. As the AC cools, it pulls humidity from the air, which condenses into water. This water should drain outside. If the drain hole or line is clogged with algae, the water backs up and leaks indoors.

Improper installation is another major cause. If the unit is not tilted slightly toward the outside, water pools inside. A worn or torn weather seal around the unit also allows rainwater and condensation to seep into the wall instead of draining away.

• Clogged drain port or line from algae and dust.
• Air conditioner not tilted correctly toward the exterior.
• Cracked or missing drainage pan inside the unit.
• Damaged or compressed foam sealing strips.
• Separated internal drain line connection.
• Ice melting from a frozen evaporator coil.