Finding water pooling around your furnace can be alarming—especially during the colder months when you rely on your heating system the most. While a furnace leak may seem minor at first, it can be a sign of something more serious, from a blocked drain line to a malfunctioning component. Addressing the issue early can prevent costly repairs, water damage, and even a complete system breakdown.

At KAC Express, we’ve helped countless Houston-area homeowners diagnose and fix furnace water leaks quickly and safely. Here’s what you need to know about why your furnace might be leaking and what to do next.

1. Condensation Issues in High-Efficiency Furnaces

One of the most common reasons for furnace water leaks is condensation—especially if you have a high-efficiency condensing furnace (typically 90% AFUE or higher).

These furnaces extract more heat during the combustion process, causing water vapor to condense inside the system. Normally, the condensation flows out through a drain line connected to your plumbing or floor drain.

But when something goes wrong—such as a clogged, cracked, or improperly installed drain line—water can begin to leak around the unit.

Signs Your Leak Is From Condensation

• Your furnace uses white PVC pipes instead of metal venting

• Water appears only when the furnace is running

• You hear dripping or gurgling sounds inside the furnace

If ignored, condensation leaks can lead to internal rust, corrosion, and electrical damage.

2. Problems With the Furnace-Connected Humidifier

If your home has a whole-house humidifier attached to your furnace, it might actually be the source of the leak.

Humidifiers rely on a continuous water supply. If the water panel becomes clogged, the drain gets blocked, or the feed line cracks, water can spill onto or inside the furnace.

Signs the Humidifier Is the Culprit

• Water pooling directly under the humidifier attachment

• Mineral buildup or rust around the humidifier

• Recent changes to your home’s humidity settings

This type of leak is common during winter when humidifiers are used most.

3. A Clogged Furnace Drain Line or Condensate Trap

High-efficiency furnaces and many modern HVAC systems use a condensate trap to capture debris before water exits your system. This trap—and the attached drain line—can become clogged with dirt, mold, or sludge over time.

Once the trap clogs, water backs up inside the system and begins leaking from saieams, panels, or drain connections.

Watch for These Red Flags

• Furnace shutting down unexpectedly

• Visible blockages or buildup in the drain tubing

• Water leaking even when HVAC appears to cycle normally

Homes with condensate pumps may also experience leaks if the pump fails or isn’t receiving power.

4. Issues With Nearby Plumbing or Appliances

Sometimes the furnace isn’t leaking at all—it’s simply in the path of water from another appliance. Because the furnace often sits in basements or utility rooms, it’s common for water from:

• A water heater

• A washing machine

• A clogged floor drain

• A leaking pipe

…to collect near the furnace and create the appearance of a leak.

How to Tell if It’s a Plumbing Issue

• Water appears even when the furnace is off

• Nearby appliances show signs of leaking

• You notice damp ceilings, walls, or pipes around the furnace area

Before assuming the furnace is the source, inspect the entire room for moisture.

5. A Damaged or Cracked Heat Exchanger (Less Common but Serious)

Although rare, a cracked heat exchanger can cause water—or moisture-like residue—to leak from your furnace. This is considered a serious HVAC emergency, as a damaged heat exchanger may allow dangerous carbon monoxide to enter the home.

Possible Warning Signs

• Water leaks combined with soot or a burning smell

• Furnace cycles on and off more frequently

• Family members experience headaches or flu-like symptoms

If you suspect this issue, turn off your furnace immediately and contact a licensed HVAC technician.

Why You Should Never Ignore Furnace Water Leaks

Even a small puddle can lead to big problems if left unaddressed. Water is one of the most damaging elements your HVAC system can encounter. Ignoring a leak may lead to:

Expensive Consequences

• Rust and corrosion on crucial internal components

• Mold and mildew, affecting air quality and health

• Electrical failures, including blown circuits or board damage

• Structural damage to flooring, drywall, or insulation

• Complete furnace failure, often at the peak of winter

Fixing the leak early is always cheaper and safer than waiting until the problem worsens.

How to Prevent Furnace Leaks in the Future

Preventing water leaks is all about regular care and system maintenance. Here’s what we recommend:

Schedule Annual Furnace Maintenance

A professional tune-up catches early signs of drain blockages, pump failures, cracked hoses, or loose connections.

Replace Air Filters Regularly

Swap filters every 1–3 months to maintain proper airflow and reduce strain on the system.

Inspect Humidifier Components

Replace water panels, check drain hoses, and ensure the humidifier is working correctly during the heating season.

Clear Floor Drains and Surrounding Wet Areas

Keeping your furnace area dry prevents water from pooling around the unit.

Routine maintenance extends your furnace’s lifespan and reduces the likelihood of an unexpected failure.

Call KAC Express for Fast Furnace Leak Repair in Houston, TX

A leaking furnace is more than a nuisance—it’s a warning sign. Whether the issue is a clogged drain line, condensate pump failure, cracked hose, or humidifier problem, the licensed HVAC technicians at KAC Express are here to help. Contact us!

We provide fast, reliable, and affordable furnace repair services throughout the Houston area, ensuring your system stays safe, dry, and efficient all winter long.

FAQs 

1. Is it normal for a furnace to leak water?

No. While high-efficiency furnaces produce condensation, water should always drain properly. Any visible leak is a sign of a problem that needs attention.

2. Can I still use my furnace if it’s leaking?

It’s not recommended. Water can damage electrical components and cause safety issues. Turn the system off and call a professional.

3. Why does my furnace leak only when the heat is on?

This usually points to a condensation issue, such as a clogged drain line or cracked tubing.

4. Can a dirty air filter cause furnace leaks?

Yes. A clogged filter restricts airflow and can lead to excess condensation inside the system.

5. How do I know if the leak is coming from my furnace humidifier?

If water collects around the humidifier attachment or you see mineral buildup, the humidifier is likely the source.