AC leaking in the attic: where the water comes from and what to do first
An air handler in the attic makes water all summer. When that water stops draining, it ends up in the insulation and then on your ceiling.
If the attic holds your air handler, a wet floor beside it is often condensate, not a roof leak. Cooling air pulls moisture out of the house, and that water should leave through a drain line. When the line clogs, the pan fills and spills. The giveaway is timing. It leaks when the AC runs, even on a dry day.
How to tell AC water from roof water
Match the leak to the weather. Roof water shows up during or after rain. AC water shows up during cooling, rain or not. Check the area too. Water directly under or beside the air handler points to the unit. Water on rafters or the underside of the deck points up.
Our find the leak tool walks through the same questions. Look from the hatch with a flashlight and do not step between the joists. Stay off the roof.
The usual suspects
Most cases come down to one of three things. The condensate line is clogged with algae or slime. The drain pan under the unit is rusted or cracked. Or the line has lost its slope or come loose, so the water has nowhere to go. A frozen coil that thaws and overwhelms the pan is another cause.
What to do first
Turn the system off at the thermostat. Running it keeps making water. If the unit has a float switch it may have shut itself down already. Put a bucket or towels under the drip if you can reach it safely from the hatch.
Then call a licensed HVAC technician. Clearing the line, replacing a pan and checking the coil are their work. Please do not open the unit or handle the electrical parts yourself. Water and wiring in a tight attic is a real hazard.
What to do about the ceiling below
If water reached the ceiling, deal with the source first. Then look at the insulation near the unit. Wet insulation loses its value and holds moisture against the wood. Our guide on wet attic insulation explains how to judge it. If a stain has formed, ceiling stains covers what to watch.
Keep it from coming back
Ask the technician about a secondary drain pan with a float switch. Have the line flushed on a schedule. A leak you catch in a week is a cleanup. A leak that runs all summer rots the framing.
Frequently asked questions
Why is my AC leaking water in the attic?
Most often the condensate drain line is clogged or the drain pan is cracked or full. The unit makes water when cooling and it has nowhere to go.
How do I tell if water in the attic is from the AC or the roof?
Check the timing. AC water appears while the system cools, even in dry weather. Roof water appears with or after rain.
Should I turn the AC off if it is leaking in the attic?
Yes. Switch it off at the thermostat so it stops making water, then call a licensed HVAC technician.
Can I clear the condensate line myself?
Leave it to a technician. Attic work is awkward, and water near electrical parts in a tight space is risky.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. A Brief Guide to Mold, Moisture and Your Home
- US EPA. Mold Cleanup in Your Home
- US EPA. Introduction to Indoor Air Quality