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AC Drain Pan Overflow: When the Ceiling Starts Dripping

The short answer

Turn the AC off at the thermostat right now — condensate production stops when the system stops. Put a bucket under any active drip, relieve any ceiling bulge with a small hole at its center, and keep people out from under sagging drywall. Then get the wet ceiling cavity inspected the same day: in Houston humidity, soaked insulation and drywall will not dry on their own. Call or text (346) 385-3496.

Why this happens in Texas homes

In most of the country, the air handler lives in a basement or utility closet. In Texas, it lives in the attic — directly above your living space. Under it sits a drain pan that catches the condensate the system produces, and in a Houston summer that can be gallons per day.

The pan drains through the primary condensate line. When that clogs (algae, biofilm — see our secondary drain guide), the pan fills. If the secondary line and float switch fail too — or were never there — the pan overflows. The only thing below it is your ceiling.

Rust matters too: metal pans corrode through after years of holding water, which produces the same result without any clog at all.

The first signs

Water stain spreading on the ceiling, usually below where the attic unit sits
Active dripping when the system runs, slowing when it stops
A sagging or bulging patch of ceiling
Musty smell in the room below the unit
In slower failures: paint bubbling or a tea-colored ring that grows over weeks

What to do right now

Thermostat off. This is the shut-off valve for condensate.
Contain the drip — bucket, towels, plastic sheet over furniture.
Relieve any bulge. A ceiling bulge is a water balloon. A screwdriver hole at the center drains it into your bucket on your schedule, instead of the ceiling failing on its own schedule.
Cut power to that room at the breaker if water is near light fixtures or the fan.
Photograph everything — the ceiling, the drips, and (if safely accessible) the pan and unit in the attic.
Get the cavity metered the same day. The visible stain is the tip; the insulation above it is the iceberg.

What NOT to do

Don't run the AC "to help dry it out." You will make more condensate and blow air through wet insulation.
Don't just repaint. We regularly open ceilings that were painted over twice while the insulation above stayed soaked.
Don't vacuum sagging drywall or push on it to "test" it.

How far did the water actually go?

This is the question that decides whether you have a $500 problem or a $15,000 problem, and you cannot answer it by looking. Attic condensate follows framing. We routinely find:

Wet insulation two and three joist bays away from the visible stain
Water tracked down inside wall cavities below the ceiling
Moisture readings at "saturated" in ceilings that looked merely shadowed

A proper inspection maps the moisture with meters and thermal imaging, then dries exactly what is wet — no more, no less — with documentation your insurer accepts.

Who to call, in what order

HVAC tech — clear the drain, verify or install float switches, check the pan for rust-through. The overflow will repeat until the cause is fixed.
Mitigation (us) — dry the ceiling cavity, verify with readings, document the loss. Same day as discovery, ideally.

If it is after hours and water is actively coming through: (346) 385-3496, 24/7.

Prevention

Two float switches (primary line and pan), a 90-day vinegar flush during cooling season, and an annual pan inspection would prevent nearly every one of these losses. The full routine: HVAC drain line maintenance for Houston homes.

Drain Pan Overflow Questions

Why is water coming through my ceiling when the AC runs?

Your attic air handler's condensate drains are blocked and the drain pan is overflowing. The water follows gravity into the insulation and drywall below. Turn the system off at the thermostat — the water production stops when the system stops.

Is a bulging ceiling dangerous?

Yes. A ceiling bulge is water pooling on top of the drywall, and drywall fails suddenly. Keep people and pets out from under it, put down a bucket, and relieve the bulge with a small screwdriver hole at its center so the water drains in a controlled way.

Can the ceiling dry on its own if I just leave the AC off?

In Houston, almost never. The wet layer is insulation and the topside of drywall inside a sealed cavity with no airflow, sitting under a hot, humid attic. It stays wet for weeks — long past the 24-48 hour window where mold begins.

What is the float switch and why didn't it stop this?

A float switch (SS1 or SS2) sits in the pan or drain line and cuts the system off when water rises. Many overflows happen because the switch was never installed, was installed only on the primary line, or failed. If you just had an overflow, have a tech verify the switch situation before running the system again.

Does insurance cover an AC drain pan overflow?

A sudden overflow event is commonly covered as accidental discharge. What complicates claims is evidence the pan had been leaking slowly for months — rust rings in the pan, layered staining. Fast action and clean documentation keep the loss in the covered category.

Do I need the ceiling replaced or just dried?

It depends on saturation and sag. Drywall that got damp but is structurally sound can often be dried in place with proper equipment. Sagging, crumbling, or repeatedly-wet drywall gets cut out. A moisture reading makes the call — not appearance.

Why does my AC drain pan keep filling up with water so fast?

In Houston summers, a working AC pulls 5–15 gallons of condensate daily. That's normal. The pan fills because the primary drain line is clogged—usually algae or biofilm buildup. The secondary line should catch overflow, but if that's missing or blocked too, the pan overflows into your ceiling. Have a tech clear the primary line and install a secondary if you don't have one.

How do I stop this from happening again after it's fixed?

First, get the primary drain line cleared and inspected for rust or damage. Second, install a secondary drain line if you don't have one—this saves ceilings when the primary fails. Third, have your HVAC tech add a float switch if there isn't one already; it shuts the system down before the pan overflows. Annual spring maintenance catches clogs before they flood you.

Standing water right now? Every hour matters.

Mold can begin developing within 24–48 hours in Houston humidity. Call or text a photo of the damage and we’ll tell you what it needs — no obligation, straight answer.

Call or text (346) 385-3496 [email protected]