What to do right now
If water is dripping or spreading across the ceiling below your air conditioner, start here.
- Turn the system off at the thermostat. An air conditioner makes water whenever it’s cooling. Switching it off stops more water from reaching an overflowing pan.
- Keep clear of wet electrical. If water is near a light fixture, ceiling fan or outlet, don’t use the switch and don’t touch the fixture. The CDC says to turn off the power at the main breaker when electrical circuits or equipment are wet or near water, but only if you can reach the panel from a dry spot. If you’d have to stand in water, call an electrician.
- Check for a sagging ceiling. A bulge or a soft, darkened patch means water is sitting on the drywall. Keep people and pets out from under it, since a waterlogged ceiling can come down. Don’t poke or cut it yourself.
- Protect what’s underneath. Put a bucket or tub under the drip. Move furniture, electronics and rugs, and cover what you can’t move with plastic sheeting.
- Take photos and video of the ceiling, the drip and anything wet. Arizona’s Department of Insurance and Financial Institutions advises taking pictures before contractors show up.
- Call an HVAC technician to fix the drain, and a restoration provider if the ceiling, insulation or flooring got wet.
If the indoor unit is in the attic, leave the inspection to the technician. Stepping off the framing can put a foot through the ceiling. If it’s in a closet, check the closet floor and move anything stored there.
Why not open the ceiling to drain it? Wiring may run through the wet area. In older homes, the EPA lists textured paint and patching compounds used on ceilings among materials that may contain asbestos, and its advice is: “If in doubt, treat the material as if it contains asbestos and leave it alone.” The EPA also says homes built before 1978 are more likely to have lead-based paint, and that cutting and demolition can create lead-contaminated dust.
Why an AC leaks through the ceiling
An air conditioner cools by passing indoor air over a cold coil. Moisture in that air condenses on the coil, drips into a drain pan below it and runs out through a condensate drain line. ENERGY STAR’s maintenance checklist warns that “a plugged drain can cause water damage in the house and affect indoor humidity levels.”
Three parts of that system can fail.
A clogged condensate drain
Debris and growth can build up in the drain line until water backs up into the pan. The Department of Energy’s Building America Solution Center notes that “a blocked drain can be unclogged and flushed out.”
An overflowing or corroded drain pan
The pan under the coil catches condensate. If the drain backs up, the pan fills and spills over. Building America also notes that older galvanized steel pans “can corrode over time,” and a rusted pan can leak even when the drain is clear. Replacing it can be a bigger job: the same source says replacing the condensate pan “often requires a total coil replacement.”
A missing or failed float switch
Building America recommends a corrosion-resistant secondary pan with “a water-level detection device that will shut off the equipment if the water level in the pan gets too high.” Technicians often call it a float switch or overflow switch. If there isn’t one, or it isn’t working, nothing stops the system while the pan overflows.
If your AC suddenly stopped cooling and there’s water in the pan, the switch may have done its job and shut the system down before the water reached the ceiling.
Where the indoor unit sits
All of this matters more when the air handler is in an attic or a closet. Building America warns that “clogged drain lines and overflowing drain pans from equipment located in attics, basements, and closets can go undetected long enough to cause severe water damage.” In an attic, the overflow lands on insulation and the back of the ceiling drywall. Often nobody knows until a stain shows up in the room below.
When it isn’t the AC
Water through a ceiling can also come from a roof leak or a plumbing line. If the drip started during or right after a storm, or it’s nowhere near the air handler, see monsoon storm water damage. If your home has an evaporative cooler on the roof, the University of Arizona’s Water Wise program notes that a sticking float valve lets the water “run continuously,” and that split seams or a rusted tray could cause a leak.
Valley conditions that add to the load
Valley air conditioners run for much of the year, which means the condensate drain works for much of the year too. A drain that’s never checked has a long season to clog.
Summer humidity adds water. The National Weather Service marks the monsoon from June 15 to September 30. Before 2008, it defined the start of the monsoon by humidity: the first of three days in a row when Phoenix averaged a dew point of 55°F or higher. Moist monsoon air gives an air conditioner more water to pull out of the house, and all of it goes through the same pan and drain line.
HVAC technician or restoration provider?
An AC leak usually needs two trades, and each has its own job.
The HVAC technician fixes the source. That can mean clearing and flushing the drain line, checking the pan and the float switch, and replacing a corroded pan. If the unit has no secondary pan with a water-level switch, ask about adding one, as Building America recommends. Ask too whether the system is safe to run while the ceiling dries. The EPA says that if an HVAC system may be contaminated with mold, you should consult its guidance before running it.
The restoration provider deals with the water that got out. Water from an attic unit soaks into insulation and the back of the ceiling drywall, and the wet patch above can be larger than the stain below. A provider will typically:
- Map the wet area with moisture meters, and often a thermal camera, from the room below and from the attic.
- Remove wet insulation. For clean-water damage, the EPA’s cleanup guidance says wet fiberglass and cellulose insulation should be discarded and replaced.
- Decide on the drywall. The EPA says drywall may be dried in place if there’s no obvious swelling and the seams are intact. If it sags, has swollen or has come apart at the seams, it’s removed and replaced.
- Dry the structure with air movers and dehumidifiers until moisture readings reach dry targets. See structural drying.
- Check for mold on framing, the back of the drywall and nearby materials. See mold remediation.
The repair and the drying often happen the same week, so tell each trade what the other is doing. Before anyone starts, look up their contractor license with the Arizona Registrar of Contractors. Our page on water heater and appliance leaks covers AC drains alongside other household leaks.
Signs of hidden moisture afterward
A ceiling can look fine once the stain dries while the insulation and framing above stay damp. The EPA advises drying water-damaged areas within 24 to 48 hours to prevent mold growth. It lists the back side of drywall, the upper side of ceiling tiles and the inside of ductwork among the places mold can hide.
In the weeks after the leak, watch for:
- A stain that comes back or grows after the drain has been fixed.
- A musty smell near the air handler or the room below. The EPA says you may suspect hidden mold “if a building smells moldy, but you cannot see the source.”
- Bubbling or peeling paint, or drywall tape coming loose.
- A ceiling that stays soft or starts to sag.
- A room that feels damp. The EPA suggests keeping indoor humidity between 30 and 60 percent to reduce mold growth.
Our guide to the signs of hidden mold covers these in more detail. If you have health concerns about mold, talk to a doctor.
How to prevent the next leak
ENERGY STAR’s maintenance checklist covers the basics:
- Check and inspect the condensate drain while the system is in cooling mode.
- Inspect, clean or change the air filter once a month.
- Get an annual pre-season check-up from an HVAC technician, and ask them to look at the drain and pan.
From Building America:
- Add a secondary pan with a water-level switch under the coil if the unit doesn’t have one.
- Ask about an older galvanized steel pan, since those can corrode over time. Building America recommends a corrosion-resistant pan.
Each time you change the filter, look at the pan or the closet floor for standing water. Catching it there is easier than drying a ceiling.
If your water heater shares the closet or garage with the air handler, our guide to a water heater leaking from the bottom explains how to tell those leaks apart. For the first steps after any leak, see what to do in the first hour.