Why Is My Furnace Leaking Water? Common Causes and How to Fix It

Noticing water leaking from your furnace can be alarming. Questions like Why is my furnace leaking water? or Is my furnace broken? are likely racing through your mind. Rest assured, you’re not alone—this is a common problem that can happen for several reasons.

Your furnace is a critical part of your home’s comfort system, especially during colder months. A water leak might not only affect the furnace but also risk damaging nearby areas of your home. The good news? Most issues causing water leaks are fixable, and some can even be handled without professional help.

This guide will walk you through the common causes of water coming out of the furnace, how to identify the problem, and when it’s time to call an expert.

How Does Your Furnace Produce Water?

To understand why water might leak from your furnace, it helps to know how the system works.

1. Heating Basics: When your thermostat signals the furnace to turn on, the furnace ignites a gas burner to generate heat.
2. Heat Transfer: Air passes over heated coils, absorbing warmth before it’s circulated through your home.
3. Condensation in High-Efficiency Furnaces: High-efficiency furnaces use a secondary heat exchanger to extract additional heat. This process creates condensation, which is drained through a system of hoses and pumps.

Key Takeaway: If your furnace is leaking water, it’s either due to condensation issues in a high-efficiency model or a related component in your HVAC system.

Air Conditioner and Furnace Leaking Water? Here’s What It Means

Experiencing both the air conditioner and furnace leaking water? That’s a sign your HVAC system has multiple issues—most commonly with drainage and airflow.

Water leaking from furnace components during AC operation may happen if:

• The drain pan beneath the evaporator coil is cracked or overflowing.
• The condensate pump has failed or is clogged.
• Air filters are dirty, causing coil freezing and excess condensation.

Homeowners often ask, why is my furnace leaking water during summer? It’s usually related to AC components, but the water damage affects the furnace housing and may even rust internal parts.

If you find both the air conditioner and furnace leaking water, act fast. Water damage around the unit can destroy insulation, warp floors, and even affect the heat exchanger over time.

Determine Your Furnace Type

Knowing whether you have a high-efficiency or conventional furnace is critical to diagnosing the issue.

High-Efficiency Furnaces

• Use a secondary heat exchanger, which produces condensation.
• Feature a PVC exhaust pipe (white plastic).
• Are common in newer homes.

Conventional Furnaces

• Do not produce condensation during normal operation.
• Feature a metal exhaust pipe.
• Are more common in older homes.

Why It Matters: High-efficiency furnaces are more likely to leak water due to condensation, while leaks in conventional furnaces typically come from other HVAC components.

Common Causes of Leaks in High-Efficiency Furnaces

If you have a high-efficiency furnace, the most common causes of water leaks are:

1. Clogged Condensate Drain Hose

• Cause: The hose that carries condensation away from the furnace can become clogged with debris.
• Solution: Inspect the hose for blockages and clean it using a thin brush or by flushing it with water and vinegar.

2. Damaged Condensate Drain Line

• Cause: Cracks, holes, or loose connections in the drain line can cause water to leak.
• Solution: Replace damaged sections or tighten loose connections.

3. Malfunctioning Condensate Pump

• Cause: If the pump fails, condensation can back up and leak around the furnace.
• Solution: Check for clogs in the pump, or replace it if it’s no longer working.

4. Cracked Inducer Assembly

• Cause: The assembly where condensation collects can develop cracks over time.
• Solution: A technician should inspect and replace the inducer assembly if needed.

5. Clogged Condensate Trap

• Cause: Not all high-efficiency furnaces have a condensate trap, but if yours does, clogs can cause overflow.
• Solution: A professional will need to check and clear the trap.

Common Causes of Leaks in Conventional Furnaces

Conventional furnaces don’t produce condensation. If you notice water, it’s usually from another part of your HVAC system.

1. Air Conditioner Drain Line or Pump

• Cause: A clogged or disconnected AC drain line or pump can cause water to pool around your furnace.
• Solution: Clean the drain line or replace the pump.

2. Cracked Drain Pan

• Cause: A damaged drain pan under the AC evaporator coil can cause leaks.
• Solution: Replace the pan to stop water leaking from the furnace.

3. Frozen Evaporator Coil

• Cause: Restricted airflow or refrigerant issues can freeze the coil, leading to leaks when it thaws.
• Solution: Address airflow issues or refrigerant levels to prevent freezing.

4. Humidifier Issues

• Cause: A cracked or clogged whole-house humidifier can cause leaks.
• Solution: Inspect and repair the humidifier’s plumbing and connections.

Check If Your AC Is Contributing to the Leak

If a furnace leaking water when AC is on, the problem likely lies in the AC system.

• Inspect the condensate pump, drain line, and evaporator coil for clogs or damage.
• Ensure proper airflow to prevent coil freezing.

Tip: Running your AC while monitoring the leak can help you pinpoint the source.

Why Is Water Coming Out Of My Furnace – Hidden Signs And What They Mean Long-Term

Most homeowners only notice a furnace leaking water when there’s already a puddle on the floor. But water damage doesn’t always start that obviously. Moisture may build up inside the unit or around it before any leak becomes visible.

So yes, do furnaces leak water? They absolutely can—especially when warning signs go unnoticed.

Here are subtle but serious signs your system is leaking:

• Rust streaks on the furnace cabinet — often from furnace leaking water from top
• Unusual sounds during operation — which may indicate internal water buildup
• Moldy smell near supply vents — from moisture traveling through ductwork
• Repeated shutdowns or tripped breakers — caused by water reaching electrical components

In many cases, why is my furnace leaking water from the top is answered by internal condensation that doesn’t drain properly. Over time, this causes corrosion on the heat exchanger or control board.

And if you’re asking do furnaces leak water even when the system seems to run fine — yes, and that’s the real danger. Silent water damage can erode parts, ruin insulation, and even void your furnace warranty.

Stay proactive. If you notice small leaks or signs of trapped moisture, schedule an inspection immediately. Catching issues early can prevent a full system failure or expensive structural repairs.

Prevention Tips to Avoid Future Furnace Leaks

Preventive maintenance can save you time and money by reducing the likelihood of leaks.

1. Schedule Annual Inspections: Regular HVAC check-ups catch issues early.
2. Clean Drain Lines and Hoses: Flush drain lines periodically to prevent clogs.
3. Monitor System Efficiency: Address unusual noises, reduced airflow, or other performance issues promptly.
4. Inspect Connections: Ensure hoses, pumps, and lines are securely attached and free of damage.

When to Call a Professional

While some issues are DIY-friendly, others require professional attention. Contact an HVAC technician if:

• You can’t identify the source of the leak.
• Water damage extends beyond the furnace area.
• Components like the condensate pump or inducer assembly need replacement.

Fix Furnace Leaks Before They Cause Bigger Problems

A furnace leaking water can seem daunting, but understanding the common causes and taking the right steps can resolve the issue quickly. Whether it’s a clogged drain line, a faulty condensate pump, or a crack in a key component, acting promptly can save you from costly repairs and water damage.

If you’re wondering, Why is my furnace leaking water? and need expert help, don’t wait. At One Hour and Heating and Air Conditioning, our skilled technicians specialize in diagnosing and fixing HVAC issues to keep your home safe and comfortable.

Schedule an inspection today to protect your furnace and enjoy peace of mind. Don’t let a small leak become a big problem—act now to safeguard your home and your comfort!