AC Unit Leaking Water Inside the House: Stop It, Find the Cause, Check the Floor

An air conditioner makes water every hour it runs. It pulls moisture out of the air on a cold coil, drips it into a pan, and sends it down a drain line to the outside or a floor drain. When you find water around the indoor unit, one step in that chain has failed. It is usually a cheap fix. The expensive part is whatever the water soaked into while nobody was looking.

Stop It First

1. 1Turn the system off at the thermostat. Every minute it runs, the coil keeps making water. Switch it to OFF, not just to a higher temperature.
2. 2Soak up the standing water. Towels or a wet vacuum around the air handler or furnace cabinet. Pull back any carpet touching the puddle so the pad underneath can breathe.
3. 3Find which step failed. Open the access panel if you can reach it safely, and look at the drain pan, the drain line and the condensate pump if there is one. The table below matches what you see to the cause.
4. 4Check what the water reached. Press the baseboards and the drywall next to the unit, look at the ceiling below if the unit sits in an attic or upstairs closet, and smell the closet. Soft, cool or musty means the water got past the floor.

Why the Indoor Unit Leaks

A clogged drain line is the most common answer. Algae and dust build up in the line over a season until it backs up into the pan. If the unit is in an attic, the overflow runs through the ceiling instead, and the AC condensate line guide covers that version.

Frozen Coil: Let It Thaw

If you see frost or ice on the lines, leave the system off and set the fan to ON so warm air melts it. Put towels down first, because a frozen coil can release a lot of water as it thaws. A filter so dirty you cannot see light through it is the usual reason, and changing it is the first thing to try. If the coil freezes again with a clean filter, the refrigerant charge needs a technician.

What the Water Reaches

Air handlers sit in closets, garages, basements and attics, usually on top of or against drywall and wood. A slow drain leak can run for days, because the unit only makes water while it is cooling. The pattern to watch for:

• Carpet and pad next to the closet. Pad holds water and does not dry in place.
• Swollen baseboards or soft drywall at the bottom of the closet wall. Water is inside the wall.
• A stain on the ceiling below an attic or upstairs unit. The ceiling cavity is wet above it.
• A musty smell when the system starts. Something near the unit has stayed wet long enough to grow.

Wet drywall and wood start growing mold in about 24–48 hours. The closet is also where the return air is pulled from, so mold growing next to the unit gets spread through the house by the system itself.

Fixing the Unit Is Not Drying the Closet

The HVAC technician clears the line or replaces the pan. That stops tomorrow's water. Last week's water is still in the baseboard, the bottom of the drywall and the subfloor, and a restoration company finds it with a moisture meter. Drying clean water runs around $3–$7 per square foot before any rebuilding. It is a small job when it is caught before the drywall has to come out.

If the floor or the wall next to your air handler is soft, (888) 840-6512 is answered 24/7 and connects you with a certified restoration company that serves your area. They give you an arrival window for your address on the call, and there is no charge for the referral.