AC Condensate Leak Through the Ceiling
The most common water loss we run in a Houston summer is not a burst pipe. It is an air conditioner quietly emptying its drain pan into a ceiling, sometimes for weeks, until a brown ring appears over the hallway. If that is what you are looking at, the first job is to stop the system making more water.
Do these first
The order matters here. Unlike a burst pipe, this leak is still being manufactured by a machine that is running right now.
- Switch the system OFF at the thermostat. Off, not auto and not fan. Every hour it runs in Houston humidity produces more condensate, and all of it is going into your ceiling.
- Cut the breaker if water is near electrical. If it is dripping around the air handler’s disconnect or through a ceiling light fixture, kill that circuit at the panel.
- Do not run it just for a bit to cool the house down. This is the one instruction people ignore, and it is the one that doubles the damage overnight.
- Catch and protect. Bin under the drip, furniture and rugs moved clear, electronics off the floor below.
- If your attic is safe to get into, empty the pan. A wet vac in the primary pan removes gallons that would otherwise keep feeding the ceiling. Do not go up there if the decking is wet or the ceiling below is sagging.
- Photograph the pan, the drain line and the stain before anything is cleaned or cleared. For this type of loss, the evidence matters more than usual.
- Call. Tell us how long the stain has been there, honestly. It changes what we recommend.
What is actually happening up there
Your air conditioner does not just cool the air, it wrings water out of it. On the Gulf Coast that is most of the work it does. A three-ton system running through a Houston August pulls something in the order of five to twenty gallons of water a day out of your indoor air, and every drop of it collects in a pan under the evaporator coil and leaves through a three-quarter inch PVC line to the outside.
That line runs at a shallow slope through a hot attic and it is permanently warm, dark and wet. It is an ideal home for algae and bacterial sludge, which builds into a plug. Once the line is blocked, the pan fills, reaches the lip and spills over the side, and in an attic installation the other side of that lip is the top of your ceiling drywall.
Your secondary protection failed, or was never there
Here is the part worth knowing, because it determines whether this happens again. The residential mechanical code requires secondary overflow protection for cooling equipment installed above a finished ceiling, and it accepts three ways of providing it:
Translate that into plain terms: if a float switch had been fitted and working, you would have come home to a hot house. That is the cheap version of this failure. A wet ceiling means the secondary protection was missing, disconnected, painted over, or had failed. Once the drying is done, fitting a working float switch is the single highest-value thing you can do to your system, and it is not an expensive part.
If you have ever seen a small PVC pipe dripping over a window or a door on a hot day and wondered about it, that was your secondary drain working exactly as designed. It is a warning, not a fault. That is the moment to call for service, before it becomes a ceiling.
How to tell it is the AC and not a pipe
| What you are seeing | What it usually means |
|---|---|
| Ring stain near the unit | A roughly circular stain directly under or just beside the air handler is the classic primary pan overflow. Water spills at the lowest point of the pan lip and soaks straight down. |
| Drip from a vent | Water coming out of a ceiling supply register is condensate tracking along the outside of a duct, or a duct sweating because its insulation has failed or come loose. |
| Comes and goes with the system | If the ceiling darkens while the system runs and dries back when it is off, it is condensate. A supply line leak does not care whether the AC is on. |
| It stopped cooling | Either the float switch did its job, or the coil iced over and then melted, which dumps far more water than the drain can carry. |
| Musty smell on start-up | Biological growth in the pan, the drain or the duct. Worth investigating even when there is no visible stain yet. |
Why this loss is treated differently from a burst pipe
A ruptured supply line is violent and obvious and you know the hour it started. A condensate leak is slow, quiet and has usually been running for a while before anyone notices. That difference changes two things, and it is better to hear them now than in week two.
1. The water is not clean
Under the IICRC S500 standard, water that has been sitting in a pan full of biofilm and then soaking through dusty insulation is Category 2, not clean supply water. That means more material comes out and less gets dried in place, because you cannot dry contamination out of a porous material. It is not an upsell, it is the difference between drying a house and drying a problem into it.
2. You are probably outside the mold window
The working window on wet paper-faced drywall and framing is roughly 24 to 72 hours. A leak that has been going for two weeks is well past it. We will tell you plainly what we find when the ceiling is opened. Where remediation is required, we work jointly with a licensed Texas mold remediation contractor and we do not take on work we are not licensed to do.
What we do, and what we do not
| Stage | What it involves |
|---|---|
| 1. Assess | Moisture mapped across the ceiling, the wall cavities below and the attic insulation, with a dry reference reading. Thermal imaging to aim the meter, never as evidence on its own. |
| 2. Contain | Because this is Category 2 water, the work area is contained and put under negative pressure before anything is opened, so what is in that ceiling does not end up in the rest of the house. |
| 3. Remove | Wet insulation out, affected drywall cut back to dry framing on a line that makes the repair straightforward. Where the readings say a section is dry, it stays. |
| 4. Clean | Affected surfaces cleaned, and antimicrobial applied where it is actually justified rather than sprayed everywhere as theatre. |
| 5. Dry | Air movers and dehumidification sized to the affected volume, with the house closed up. Houston outdoor air is wetter than what you are trying to dry for most of the year, so ventilating with it works against you. |
| 6. Document | Readings logged daily against the reference area until materials hit dry standard, with photographs throughout. You get the logs. |
What we do not do is HVAC. Clearing the drain line, fitting or replacing the float switch, servicing the coil and diagnosing why the system iced up is your air conditioning company’s work, and we will coordinate with them rather than talk over them.
Stopping it happening again
This is the most preventable water loss in a Houston home, and almost all of it is maintenance you can do or ask for.
| Do this | Why |
|---|---|
| Vinegar, monthly | A cup of distilled white vinegar down the capped access tee on the drain line, once a month through cooling season. It keeps the biofilm from establishing. Vinegar rather than bleach, which is harsher on glued joints and on a metal pan. |
| Ask about your float switch | Ask your HVAC technician directly whether you have one and whether it was tested. Plenty of Houston homes built before it was routinely enforced simply do not have one. |
| Find your secondary drain | Know where it terminates. If it drips somewhere nobody ever looks, it is not doing the job the code intended. |
| Look in the pan each spring | Rust, standing water or sludge in the auxiliary pan means the primary side is already struggling. |
| Fix icing and short-cycling | A system that ices and thaws produces far more water in bursts than the drain line was designed to carry away. |
Questions people ask us on this call
Can I clear the drain line myself?
Often, yes. Find where the small PVC line ends outside, hold a wet vac tightly over it and run it for two or three minutes to pull the blockage backwards. If that does not free it, stop there. Pushing air or water down the line from the attic end is how people blow a glued joint apart inside a ceiling, which turns a clog into a flood.
Is the black slime in the pan mold?
Usually it is biofilm, a mix of algae, bacteria and household dust that thrives in a warm wet pan. Whether there is mold growing in the ceiling assembly above is a separate question, and it gets answered by opening it up and looking, not by guessing from the pan.
The ceiling is stained but not sagging. Does it really need replacing?
The meter decides, not the look of it. Paper-faced drywall that has been wetted and partly dried repeatedly over several weeks is often compromised even when it still looks flat and sound. Where readings come back dry and the cavity above is clean, we leave it alone and say so.
Should I get a mold test?
If you can already see growth, a test mostly confirms what is in front of you and delays the work. Testing earns its keep in two situations: clearance after remediation, and cases where someone in the house is reacting but nothing visible can be found. We do not sell testing, so we have no reason to push it either way.
Do you fix the air conditioner too?
No, and we will not pretend otherwise. We handle the water and the structure: extraction, removal, cleaning, drying and documentation. Clearing the drain, fitting or replacing a float switch and servicing the unit is your HVAC company’s work. We are happy to coordinate so the two do not trip over each other.
How long will the drying take?
For a single ceiling and the wall below it, usually three to five days of equipment once the removal is done. Longer where the leak ran for weeks, where cabinets or hardwood are involved, or where the affected area runs across more than one room. We read the materials daily against a dry reference elsewhere in the house and pull equipment off each area as it reaches standard, rather than leaving everything running for a round number of days.
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If it is not actively pouring, leave your details and how long the stain has been there. We will call you back and tell you what we would do in your position.