Water is coming out of a vent.
Water at a vent is not condensation on the grille. Something upstream is overflowing.
Water at a ceiling vent means something above it is overflowing and the duct is carrying the water to the nearest opening. That is almost always the drain pan under an attic air handler.
First ten minutes
- Turn the system off at the thermostat. Not just the cooling, the fan too. Every minute it runs makes more water.
- Put something under it. A bucket, towels, a tarp.
- Move what is underneath out of the way.
- Do not punch the ceiling to drain a bulge unless it is clearly about to come down. If you do, stand to the side.
- Photograph everything before anything gets cleaned up. Insurance and any claim will want it.
What is actually happening
An air conditioner condenses moisture out of your air by design. That water runs into a pan and leaves through a PVC drain line. When the line plugs with algae and dust, the pan fills.
Most systems have a float switch that shuts the system down before the pan goes over. If you have water on the ceiling, either there is no switch, the switch failed, or somebody bypassed it.
The other common path: a secondary drain pan under the unit that has rusted through, or a secondary line that was never connected.
The one that is not the drain
Ice. A coil that freezes and then thaws releases far more water at once than the pan was built to carry, and it will overflow a drain that is perfectly clear. If you have seen frost on the copper lines, the drain is a symptom and the frozen coil guide is the actual problem.
What it costs on the AC side
Clearing the line and replacing a failed float switch are both flat prices already published. Where the unit sits below the drain and the water has to be lifted, a condensate pump is its own flat price.
The drywall and paint are not an HVAC bill, and they are the reason to act in the first ten minutes rather than the first ten hours.
Stopping the next one
A cup of white vinegar down the condensate access tee every couple of months through cooling season prevents most of this. If your system has no float switch, fitting one is cheap and its entire job is preventing exactly this bill.
Questions that come with this one.
Should I turn the AC off?
Yes, at the thermostat, immediately. Running it keeps producing water and keeps whatever is overflowing overflowing. A warm house for a few hours is cheaper than a ceiling.
Could it just be condensation on the vent itself?
It can be, in monsoon season, when humid air meets a cold metal register. That shows up as beads on the grille rather than a drip, and it does not stain the ceiling. A spreading brown ring is not condensation.
Is it going to cost a fortune?
The AC side of it usually does not. A drain clear-out and a float switch are both flat prices on the list. What costs is the drywall, insulation and paint, which is why shutting the system off quickly matters.
Other things that go wrong.
There is ice on the outdoor unit.
Winter frost on a heat pump is routine. Summer ice outside is not, and it points somewhere specific.
Read itDownstairs is fine. Upstairs is not.
Heat rises, the roof is the hottest thing you own, and one system for two floors is a hard ask here.
Read itThe bill doubled and nothing feels different.
Usually the AC, occasionally the rate plan, and the AC version is often cheap to fix.
Read it