AC Leaking Water Inside the House? Causes and What to Do Now

Quick answer: Most indoor AC leaks come from a clogged condensate drain line, a cracked or rusted drain pan, a frozen coil melting, or a failed condensate pump. Turn the AC off at the thermostat, protect floors and ceilings, replace the filter and check the drain outlet outside. If water keeps backing up, the pan is damaged or the unit is in the attic, call for service before the water causes more damage.

Finding water pooling around your furnace or air handler, or a brown stain spreading across the ceiling under the attic unit, is stressful. The good news: most indoor AC leaks have a handful of common causes, and acting quickly limits the damage. Here's what's happening and what to do.

Why air conditioners make water

Your AC is also a dehumidifier. As humid air passes over the cold indoor coil, moisture condenses and drips into a drain pan, then flows out through a condensate drain line to the outside, a floor drain or a condensate pump. On a humid Jersey Shore day, a system can remove a surprising amount of water. When anything interrupts that path, water ends up where it shouldn't.

Step 1: Do this right now

1. Turn the AC off at the thermostat. This stops more condensation from forming.
2. Protect the area. Towels, buckets, a wet/dry vacuum; move belongings away.
3. If water is near electrical outlets or the unit's wiring, switch off the breaker for the air handler/furnace if it's safe to reach.
4. For a ceiling bulge filled with water, place a bucket underneath; a small puncture to drain it can prevent a larger collapse, but be careful and keep clear.

The most common causes

1. Clogged condensate drain line

Algae, sludge, dust and debris grow inside the drain line, especially in warm, humid months. When it clogs, water backs up into the pan and overflows. This is the number one cause of indoor AC leaks.

2. Cracked, rusted or shifted drain pan

Older metal pans rust through; plastic pans can crack. If the pan itself leaks, even a clear drain won't stop the water.

3. Frozen evaporator coil

When a coil freezes (often from a dirty filter or low refrigerant), the ice eventually melts all at once, overwhelming the pan. If you see ice, read why is my AC freezing up.

4. Failed condensate pump

Basement and some attic systems use a small pump to push water out. If the pump fails or its float sticks, water overflows the reservoir.

5. Disconnected or poorly sloped drain line

Lines can separate at fittings, or sag so water collects instead of draining.

6. Tripped or missing float switch

Many systems have a float switch that shuts the AC off when water backs up. If your AC suddenly stopped cooling and the pan is full, the switch did its job. If there's no switch on an attic unit, it's worth adding one.

What you can safely check

• Filter: replace it if dirty.
• Drain outlet: find where the line ends outside and look for a trickle when the AC runs. If nothing comes out, it may be clogged.
• Wet/dry vacuum trick: with the system off, hold the vacuum hose tightly on the outdoor end of the drain line for a minute or two to pull the clog.
• Condensate pump: check that it's plugged in and the reservoir isn't overflowing.

If water keeps backing up, the line runs through walls, or the pan is damaged, call for AC repair.

Leak damage and mold

Ongoing moisture in ceilings, drywall and insulation can lead to mold, especially in humid shore homes. Dry wet areas thoroughly with fans and a dehumidifier, and keep an eye on stains that don't go away. Our humidity control guide has more tips.

How to prevent AC leaks

A spring tune-up includes clearing the drain and checking the pan and safety switch. That's why our $89 tune-up and Prime Comfort Club membership ($19/month for two tune-ups a year) prevent so many summer leaks.

Attic air handlers need extra protection

Many New Jersey homes, especially Cape Cods, split-levels and newer two-story homes, have the air handler in the attic. When a drain clogs there, water comes through the ceiling, damaging drywall, insulation and belongings below. Three safeguards make a big difference:

1. Secondary drain pan under the unit to catch overflow.
2. Float safety switch that shuts the AC off when water rises in the pan or line.
3. Separate secondary drain line that ends somewhere visible, like over a window, so you notice when the main line is clogged.

If water ever drips from that secondary line, it means the primary drain is blocked. Call for service before the pan overflows.

Condensation on ducts and vents

Not every drip is a drain problem. In humid weather, cold supply ducts and vents can sweat if they run through hot, damp attics or crawl spaces without proper insulation, or if supply air is very cold because of low airflow. Water stains near ceiling vents can be condensation rather than a leak. Insulating ducts, sealing air leaks around vents and correcting airflow usually solve it. Keeping indoor humidity in check helps too.

Help when your AC is leaking

Water damage gets worse by the hour, so don't wait. We serve Brick, Point Pleasant, Berkeley Township, Neptune and all of Ocean, Monmouth and Burlington counties, with same day service and 24/7 emergency help. Message us on WhatsApp or call, and we'll find the source and fix it right with upfront pricing.