AC Leaking Water Inside the House: Causes and What to Do
Quick answer: An AC leaking water inside the house is usually caused by a clogged condensate drain line, a frozen evaporator coil, a cracked or rusted drain pan or a failed condensate pump. Turn off the system, clean up the water, clear the drain or call an HVAC tech, and dry any wet ceiling or drywall quickly. For stains and sagging, see ceiling water damage repair.
Air conditioners pull moisture out of the air as they cool it. That water drips off the indoor coil into a drain pan and runs out through a condensate line. When any part of that path fails, water ends up on the floor, in the wall or through a ceiling. Colorado's dry air means AC units here produce less water than in humid states, but a clog still adds up to real damage over a few hot weeks.
Common causes of an AC leaking inside
| Cause | What you'll see | Fix |
|---|---|---|
| Clogged condensate drain | Water around the indoor unit, full drain pan | Clear the line with a wet vac or have it flushed |
| Frozen evaporator coil | Ice on the coil or refrigerant line, water when it melts | Change the filter, check airflow, call HVAC for low refrigerant |
| Dirty air filter | Weak airflow, coil freezing | Replace the filter every 1–3 months during cooling season |
| Cracked or rusted drain pan | Water under the unit even with a clear drain | Replace the pan |
| Failed condensate pump | Water around a basement unit with no gravity drain | Replace or repair the pump |
| Disconnected drain line | Water in the wall or ceiling near the line | Reconnect and secure the line |
| Missing or failed float switch | Attic pan overflows into the ceiling | Install or replace the safety switch |
What to do right now
- Turn off the AC at the thermostat and, if needed, at the breaker or service switch.
- Clean up standing water with towels or a wet vac.
- Check the drain pan. If it's full, the drain is likely clogged.
- Check the filter. A clogged filter can freeze the coil.
- Look for ice. If the coil is frozen, leave the system off so it can thaw, with a pan or towels underneath.
- Look up and around. Check ceilings below attic units and walls near the drain line.
- Take photos of any damage.
Where AC leaks cause water damage
Basement units. The furnace and AC coil often sit in a basement utility room. A leak can soak carpet and drywall in a finished room next door, and sit unnoticed for weeks.
Attic units. Some homes, especially newer two-story homes and remodels, have the air handler in the attic. A pan overflow there leaks straight through the ceiling.
Closet units. In condos and apartments, the air handler is often in a closet. Water can run under the wall into the next room or into the unit below.
Evaporative coolers. Many older Colorado homes still use roof-mounted swamp coolers. They use a steady supply of water, and a stuck float or a cracked pan can leak through the roof.
Signs of a hidden AC leak
- A musty smell when the AC runs (what a musty smell means)
- Ceiling stains in rooms below the attic unit
- Damp carpet near the furnace or air handler
- Peeling paint or swollen baseboards near the indoor unit
- Water around the base of the unit after long cooling days
Preventing AC leaks
- Replace air filters regularly during cooling season
- Have the system serviced each spring, including the drain line
- Pour a cup of diluted vinegar or water down the condensate line access monthly in summer, if your technician recommends it
- Make sure attic units have a secondary drain pan and a float switch
- Install a water sensor near the indoor unit
- Drain and winterize evaporative coolers each fall
When to call a pro
Call an HVAC technician for frozen coils, refrigerant problems, cracked pans and failed pumps. Call a water damage restoration company if water soaked a ceiling, drywall, insulation or carpet. Ceiling drywall that stays wet can sag and grow mold, and wet insulation above it rarely dries on its own. Our guide to the water damage restoration process explains how ceilings and walls are dried.
AC leak soaked the ceiling or carpet? Call and we'll dry it before mold takes hold.
Call (303) 879-1370Frequently asked questions
Is it normal for an AC to drip water?
It's normal for an AC to produce water, called condensate, and send it outside or to a drain through a line. It's not normal for water to collect around the indoor unit or drip from a ceiling.
Can I still run my AC if it's leaking?
Turn it off until you find the cause. Running it with a clogged drain or frozen coil can make the leak worse and damage the equipment.
How do I unclog an AC condensate drain line?
Turn off the power to the system, find the drain line access, and use a wet vac on the outdoor end to pull out the clog. Many technicians also flush the line with water. If you're not comfortable doing it, call an HVAC technician.
Why is my AC leaking water from the ceiling?
If the air handler is in the attic, a clogged drain or overflowing drain pan can leak through the ceiling below. Some attic units have a safety float switch that shuts the system off when the pan fills; if it's missing or failed, water can overflow.
Can an evaporative cooler leak into the house?
Yes. Swamp coolers on the roof use a lot of water. A cracked pan, a stuck float valve or a bad roof seal can send water into the ceiling. Drain and winterize roof coolers each fall.
Sources
Related guides
Musty Smell in the House: Causes and Fixes
A musty smell almost always means moisture. Here's where to look, how to fix it and when it points to hidden mold.
The Water Damage Restoration Process, Step by Step
What happens from the first phone call to the final coat of paint, and the difference between mitigation and restoration.
AC leak stained the ceiling?
Turn the system off and call. We'll dry the ceiling and walls before mold starts.