Water Dripping From Furnace or Air Conditioner: Causes and Solutions

The appearance of water from a furnace or air conditioner is a common homeowner concern that can indicate benign condensation or a developing HVAC problem. This article explains why HVAC systems produce water, identifies common causes of leaks, provides step-by-step troubleshooting, and offers maintenance and cost guidance to resolve issues efficiently.

Symptom	Likely Cause	Quick Fix
Pooling Near Furnace	Condensate drain blockage or cracked drain pan	Clear drain, replace pan if corroded
Water Under Indoor AC Unit	Clogged evaporator coil drain or frozen coil	Thaw coil, clear condensate line
Discolored Ceiling Stains	Condensate overflow from air handler or duct leak	Inspect ducts, repair or call pro
Sudden Heavy Leak	Failed condensate pump or burst pipe	Turn off system, call technician

How HVAC Systems Produce Water

Both furnaces and air conditioners can generate water as part of normal operation. An air conditioner removes humidity from indoor air by cooling it across an evaporator coil, causing moisture to condense into a drain pan and flow through a condensate line.

High-efficiency gas furnaces also produce condensate because combustion and exhaust heat-exchange processes cool combustion gases below the dew point. That condensate collects and drains away from the furnace through a dedicated condensate line.

Key point: Some water is normal, but visible leaks or pooling indicate a problem with collection or drainage components.

Common Causes Of Water From Furnace Or Air Conditioner

Clogged Condensate Drain Line

The most frequent cause of leaks is a clogged condensate drain line. Algae, mold, or debris can build up inside the PVC drain, preventing water from flowing to the drain or condensate pump, causing overflow.

Cracked Or Rusted Drain Pan

Older metal drain pans can corrode and develop holes, while plastic pans can crack from stress or freezing. Once the pan fails, water escapes instead of being routed to the drain line.

Frozen Evaporator Coil

Restricted airflow, low refrigerant, or a dirty coil can cause the evaporator coil to freeze. When the system shuts down, the ice melts quickly and produces large amounts of water that may overwhelm the drain.

Failed Condensate Pump

Systems located below drain level, such as basements, rely on a condensate pump to move water to the household drain. If the pump fails or its float switch sticks, water will back up and leak.

Improper Installation Or Tilt

An air handler or furnace must be level enough for condensate to reach the drain. Incorrect installation, sagging ductwork, or shifting equipment can redirect water to the floor or nearby framing.

Blocked Air Filter Or Poor Airflow

Dirty or obstructed filters reduce airflow across the evaporator coil, risking coil freezing and subsequent melting-related leaks. Restricted airflow also raises indoor humidity, increasing condensate volume.

Leaking Humidifier Or Steam Components

Some furnace systems include humidifiers or steam generators that can leak due to broken fittings, cracked reservoirs, or worn seals, producing water near the furnace.

Troubleshooting Steps Homeowners Can Do

Safety First

Before any inspection, turn off the HVAC system at the thermostat and switch off power at the breaker if accessing internal components. For gas furnaces, consider shutting off the gas if water is contacting electrical parts.

Inspect Visible Drain Lines And Pans

Look for standing water, discoloration, corrosion, or cracks in the drain pan under the evaporator coil or furnace. Trace the condensate line to where it exits the equipment and check for blockages or kinks.

Clear The Condensate Line

Use a wet/dry vacuum at the condensate line exit or access port to pull debris and algae out of the line. Pour a cup of household bleach diluted in water or a commercial HVAC condensate treatment down the drain port to inhibit future growth, then flush with water.

Check And Replace Air Filters

Inspect filters and replace if dirty. A clean filter improves airflow, reducing the chance of coil freeze-up and subsequent leaks. Replace filters per manufacturer’s recommendations or monthly during heavy use.

Examine The Condensate Pump

If the system uses a condensate pump, check for proper operation. Ensure the pump is plugged in, the float moves freely, and the discharge line is clear. Replace a noisy or non-operational pump.

Look For Frozen Coils

Frosted or iced coils indicate restricted airflow or refrigerant issues. To confirm, shut off the system and allow the coil to thaw. Once thawed, clear the condensate drain and schedule professional service to address underlying causes.

Test Safety Switches And Float Switches

Many systems have float switches to shut down the HVAC if the condensate drain overflows. Test the switch by lifting the float—if the system does not shut off or the switch fails to reset, it may need replacement.

When To Call A Professional Technician

Call an HVAC professional if the source of water cannot be located, the evaporator coil is frozen repeatedly, refrigerant leaks are suspected, or there is water contacting electrical components. Also seek help for gas furnace combustion or venting concerns.

Urgent attention is required for significant leaks, structural water damage, mold growth, or if water has reached electrical panels or controls.

Preventive Maintenance To Avoid Future Leaks

Schedule annual HVAC inspections that include cleaning the evaporator coil, testing the condensate pump, and inspecting drain lines and pans for corrosion. Regular preventive maintenance reduces the risk of leaks.

Install an access port and a clear trap in the condensate drain line to facilitate periodic flushing and vacuuming. Consider adding a condensate overflow safety switch if one is not present.

Use routine condensate treatments: a monthly or quarterly biocide tablet or treatment can prevent algae and mold from clogging the drain line.

Cost Expectations For Repairs

Minor DIY tasks like clearing a condensate line or replacing a filter can cost under $100. Professional cleaning and drain line servicing typically range from $100 to $300 depending on region and complexity.

Replacing a condensate pump usually costs $150 to $400 installed. Replacing a drain pan or repairing an evaporator coil can range from $300 to over $1,200. Major repairs such as refrigerant leaks or coil replacement may exceed $1,000.

Tip: Obtain multiple quotes and ensure the technician inspects for root causes, not just symptoms, to avoid repeat failures.

Damage Control And Mold Concerns

If water has been present for more than 24–48 hours, inspect for mold on drywall, insulation, and wooden framing. Mold can begin to grow quickly in warm, moist conditions.

Dry affected areas thoroughly with fans and dehumidifiers and remove saturated insulation or porous materials that cannot be cleaned. For extensive mold or structural damage, contact a remediation specialist.

FAQ

Can A Furnace Leak Water During Normal Operation?

Yes, high-efficiency furnaces produce condensate during normal operation. The condensate should drain through a dedicated line. Visible leaks indicate a drainage or collection issue.

Why Is My AC Leaking Water Inside Instead Of Outside?

Most central AC systems are designed to drain condensate to a nearby drain or outside. If the line is clogged, the pan overflows and water spills inside. Improper installation or a cracked pan can also cause indoor leaks.

Is It Safe To Keep Running The System If It’s Leaking?

It is not recommended. Continued operation can cause electrical damage, mold growth, and structural harm. Turn off the system and power while investigating the cause.

How Often Should The Condensate Line Be Cleaned?

Cleaning the condensate line at least once a year is a common recommendation. Homes in humid climates or systems showing slow drainage should have the line cleared more frequently.

Resources And Tools For Homeowners

Useful tools include a wet/dry vacuum, basic hand tools, a coil-cleaning spray, replacement filters, and a small torch-safe inspection light. For condensate treatment, purchase HVAC-specific biocide tablets or bleach diluted per manufacturer guidance.

Refer to equipment manufacturer manuals for model-specific condensate system layouts and recommended maintenance intervals. For gas furnace condensate or venting concerns, prioritize licensed HVAC or gas technicians.

Final Practical Checklist

• Turn Off Power Before Inspecting Internal Components.
• Check And Replace Dirty Air Filters Regularly.
• Inspect Drain Pans For Corrosion Or Cracks.
• Clear Condensate Drain Line With A Vacuum And Flush.
• Test Condensate Pump And Safety Float Switches.
• Schedule An Annual Professional HVAC Tune-Up.

Addressing water from a furnace or air conditioner early reduces repair costs and prevents property damage. Routine maintenance, timely troubleshooting, and professional assistance when needed preserve efficiency and safety of HVAC systems.