AC Leaking Water Inside the House: How to Fix It
Water drips from the indoor air handler/furnace area, pools on the floor nearby, or the AC shuts itself off unexpectedly.
DIY Cost
$0–$15
Typical Pro Cost
$150–$300
Tools Needed
- Wet/dry shop vacuum
- Funnel
- Towels
Parts Needed
- Distilled white vinegar or a condensate-line cleaning tablet
⚠️ Safety Warnings
- Turn off the AC system before working on the condensate line or drain pan to avoid it running while water is actively draining incorrectly.
- Standing water near the furnace/air handler and its electrical connections is a shock hazard — dry the area before doing anything else.
Step-by-Step Instructions
Understand what's causing it
AC units remove humidity from the air as condensation, which normally drains out through a condensate line to the outside or a floor drain. A clogged line (algae/mold buildup is common) is by far the most frequent cause of indoor water leaks.
Find the condensate drain line
It's usually a white PVC pipe running from the indoor unit to outside the house, or to a nearby drain/pump. Look for the point where it exits, and check if water is dripping there normally or not at all.
Check the drain pan for cracks
If your system is accessible, look at the drain pan under the indoor coil for visible cracks or rust-through — a damaged pan leaks regardless of whether the line is clear, and needs replacing rather than clearing.
Clear the line with a wet/dry vacuum
At the outdoor end of the drain line, attach a wet/dry shop vacuum (with a rag around the connection to seal it) and run it for 2-3 minutes to suck out the clog. You'll often see algae/sludge come through.
Flush the line
Find the access point near the indoor unit (often a T-fitting with a cap), remove the cap, and pour a cup of distilled white vinegar down the line using a funnel. This helps break down algae buildup and slows future clogs.
Run the AC and confirm it drains properly
Run the system for 20-30 minutes and check that condensation is draining normally at the outdoor exit point, with no new water appearing indoors.
When to Call a Professional
If the drain pan is cracked, if clearing the line doesn't stop the leak, or if you can't locate/access the condensate line safely, call an HVAC technician — a cracked pan needs replacement, and repeated indoor leaking can lead to real water damage if it's not fully resolved.