Why Is My Furnace Leaking Water? How To Fix It [With Pictures]

Water damage is one of the most common household disasters. A water leak can be a major headache and even cause bio-growth to grow. This will make you sick and cost a lot of money to repair.

However, we've all been there, as a furnace leaking water is a common problem for homeowners to deal with. A water leak from your furnace could lead to high repair costs; and even worse, if it does produce bio growth, this could damage your property and pose a severe risk to your health. If it continues to leak, your furnace will eventually fail and need to be replaced.

It's always better to address a water leak early before it becomes a problem. An unchecked furnace leak can lead to more costly repairs down the road, so homeowners should never overlook it. This post provides information on why furnaces leak water and what can be done about it! Call now so that we can stop the problem before it becomes bigger issue.

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How Does My Gas Furnace Work And Does it Produce Water?

You may be wondering, "what does a water have to do with my furnace?" Let's jump right in so we can explain how!

For starters, lets dig into how your furnace works. When the indoor temperature dips below the thermostat's set temperature, the thermostat sends a signal to the control board inside the furnace to begin the heating cycle. This starts by turning on an ignition switch, opening the gas valve, and turning on the draft fan to create combustion. The combustion warms the heat exchanger. The flue gases inside the heat exchanger are released outside through the exhaust pipe. After this, the blower fan blows cool air from inside your home past the heat exchanger. This is where the air absorbs the heat and is then forced through your house's ventilation system to heat the house. That's how warm air is made!

Additionally, if your furnace is struggling to turn on at the start of the cold season, consult our blog to learn more!

Got the basics? So where does the water come in?

A conventional furnace, also known as a standard efficiency furnace, does not produce water. However, if you have a high efficiency furnace, (90% efficiency), condensation will arise due to the addition of the second heat exchanger. This is why a high efficiency furnace is also known as a condensing furnace, and a standard efficiency furnace is a non-condensing furnace.

heat exchanger

Primary Heat Exchanger

After the burning gas exits the primary heat exchanger, it proceeds to the secondary heat exchanger. The secondary heat exchanger is where the exhaust or flue gas undergoes further heat transfer. This creates water vapor. Find out more about cracked heat exchangers in our blog about them! As water transitions from a vapor to a liquid, more heat is released into the secondary heat exchanger. In this way, the furnace functions even more efficiently. From there, the condensation is drained into a condensate pump or a floor drain.

What kind of furnace unit do I have?

Now, let's figure out the type of furnace you have.

It is relatively easy to identify your furnace type and narrow down the reason for its leak. Look at the exhaust pipe. If it is white plastic furnace PVC pipe, then it is a condensing furnace, making it high efficiency. A metal exhaust pipe has a standard efficiency rating and does not produce condensation.

Standard Efficiency vs high efficiency furnace

Why is High efficiency furnace Leaking Water?

When a high efficiency furnace releases the exhaust gases, condensation is created. This condensation is a significant amount of moisture on the PVC pipe and needs to be drained into either a floor drain or a condensation pump. A water leakage occurs when the condensation is unable to drain properly.

Let's provide some examples:

Leaking From Condensate Drain Hose

The drain hose, which slopes down from the PVC exhaust pipe, can easily become clogged with debris, dirt, and dust. If any tubing that aids the draining is damaged, disconnected, or clogged, this is when a condensation leak occurs.

drain hose

Condensate Drain Hose

Inducer Assembly Leaking

Next, the condensation runs down the exhaust / flue pipe, through the condensate drain hose, and into the inducer assembly. If the inducer assembly is cracked, water can leak out of the furnace.

Leaking From Condensate Drain Line

As the water exits, it passes through a condensate drain line. If this has a loose connection, cracks, or holes, it can cause water leakage. Also, if the drain line is clogged, it can cause the condensate to back up and create a water leak.

clogged drain line Baltimore MD 726103 st

Leaking Out Of The Condensate Trap

A clogged condensate trap can cause condensate to back up and overflow out of the furnace. Note, not all high-efficiency furnaces have a condensate trap.

Condensate Pump Leaking

The condensate pump is where the condensate eventually drains into. This is yet another component that can clog and lead to a leak. A blocked drain, or even a partially blocked drain, will result in the furnace leaking. If you notice water on the floor around your high efficiency furnace unit, or water or rust stains within the cabinet, your furnace is not draining properly. Similarly, a malfunctioning pump can cause water to back up and create a furnace leak. In this situation, a professional will have to replace it. Most condensate pumps last 3-5 years; after that, they tend to not perform as optimally.

condensate pump leaking water

Overflowing condensate pump

Why is Non-High Efficiency Furnace Leaking Water?

If your furnace unit is a conventional furnace operating at standard efficiency, then it will not generate any water. If there is standing water around your furnace, it is probably coming from another appliance.

 Here are a few appliances to look out for:

Water Leaking From Air Conditioner

When your AC unit is running, it generates water, making it a common source of leaks. Your AC may leak for a number of reasons, such as:

Damaged Drain Pan

All AC units have a primary drain pan located under the evaporator coil. Some AC units also have a secondary drain pan beneath the unit. The purpose of the drain pan is to catch any condensate. If there is a crack or hole, the excess water will spill or leak out.

water leaking from drain pan

Water leak from attic drain pan

A Frozen Coil

If your evaporator coil freezes, your AC unit will leak. 

frozen coil

Frozen Evaporator Coil

Clogged Drain Line

A clogged drain line will cause the drain to disconnect from the drain pan if water cannot pass through. The water will then drip and pool around your AC. 

Failed Condensate Pump

A condensate pump is necessary to drain the condensation from the HVAC. If you have a high-efficiency furnace, the furnace and air conditioner most likely share the condensate pump.

Learn more in our AC leaking water blog!

Water leaking From Hot Water Heater

The culprit could also be your water heater. In time, the drain valve or T&P valve can loosen, which can allow water to seep out. Additionally, any crack in your water heater will cause it to leak. Unfortunately, the corrosive effect of hard water can cause cracks to form. Learn more about what causes your water heater to leak and what you can do about it in our blog on the subject!

Water Leak From Humidifier

Another reason you may see water on the ground is if you have a whole-house humidifier. An HVAC system with a built-in humidifier will require plumbing to supply water to the humidifier. A leaking humidifier can occur when the water lines crack, break, or get clogged due to lack of maintenance.

Is Furnace Leaking Water Dangerous?

Water can be destructive. A leaking furnace may not pose an immediate risk to your safety, but it certainly puts your comfort on the line. If a leaking furnace is left untreated, you will undoubtedly be facing cold and costly outcomes.

Dripping water can lead to rust developing. Rust decays the working parts of your furnace, first contributing to lessened efficiency and eventually leading to breakdowns and repairs. For a guide to some possible repairs that you may need a professional to address, check out our furnace repair blog.

water leaking inside furnace

Cleaning up a furnace leaking water. Rust has formed from the water leaking.

The most dangerous place for rust to develop is on the heat exchanger. If rust develops a hole or crack on your heat exchanger, your home or business could be exposed to the harmful CO gas. A cracked heat exchanger can have serious repercussions on your health, not to mention your wallet.

rusted and cracked heat exchanger

rusted and cracked heat exchanger

Water leaking inside the furnace can also cause damage to the internal electrical components. This can cause your furnace to stop working altogether. The circuit board, for example, is responsible for transmitting the signals needed to start the furnace's heating procedure. If water leaks on to the circuit control board, it won't be long before you need to replace it!

Rust on furnace control board

Rust on furnace control board

furnace leaking water on control board

furnace leaking water on control board

A leaky furnace can lead to more serious consequences if it is not fixed in time. You might still have heat, but it won't last for long. Call for a furnace repair before things get worse.

What Should I do If I Have A furnace leaking water 

Don’t Panic!

Step 1. Turn the HVAC system off.

Furnace switch

First, turn off your furnace. This stops more water from leaking. You can do this by turning it off from the thermostat. Or you can turn the furnace switch off. You should see a switch on or next to the furnace that looks identical to a light switch. If you can’t find it, turn the unit off from the breaker.

Step 2. Clean up water around the furnace

furnace leaking water

Cleaning up a furnace leaking water 

Next, clean up all the water you can. You can do this with towels and napkins. If it is a substantial amount of water, you may even consider a wet vac.

Step 3. Unscrew the front panel of the furnace

Remove furnace door

Remove furnace door

You can unscrew the front panel of the furnace to clean up the water inside (if you feel comfortable). It's always important to stay proactive on mold prevention. 

Step 4. Call An HVAC Pro

The last step is always to call a technician. A furnace that is leaking water will only get worse with time, so don't wait!

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How can I prevent my furnace From leaking water in the future?

If you have a leaking furnace, it can be expensive to repair. Luckily, this doesn't need to happen! The good news is that there are proactive steps you can take to prevent leaks from occurring, the most important of which is scheduling routine maintenance. HVAC professionals can spot signs of impending problems before they happen - like leaks or clogs that could make for costly repairs later on. We can help prevent future issues by performing regular maintenance on your system by diagnosing the cause of the leak and figuring out the best way to fix it. Learn about what happens during a furnace tune up and how you can perform maintenance on your furnace by consulting our blog. Schedule an appointment today and get peace of mind knowing that if something does go wrong down the road, we’ll have already addressed any potential issues! 

We Have Your Back

If you have a leaky furnace, it’s important to get the problem fixed as soon as possible. The longer your heating unit is leaking water and losing energy efficiency in the winter, the more likely it will be for you to experience other problems with your home or property. So, if you find that your furnace is leaking water or not heating your home, don’t hesitate to call Baltimore's best furnace repair company. Don't let another day go by without getting that pesky leak taken care of. Every minute wasted only makes things worse when it comes time for a furnace repair. Schedule online or call our experts today so we can repair your leaky furnace before anything else goes wrong! 

Contact us today if you have questions about a leaky furnace—or if you simply want more information about how to keep your home safe and healthy. We offer furnace repairfurnace maintenance, and new furnace installation.

  • Your article is really great. Thanks for sharing valuable information with us. We also provide best field service management software.

  • Furnace leaks can be overly exaggerated & sometimes it’s the last technician who came in to replace the pump is the cause of a PVC pipe leak!

    • Hey there! Thanks for joining the conversation and sharing your thoughts with us. It’s always great to hear different perspectives on furnace maintenance and repairs. While we can’t speak to the specifics of your situation, we understand how frustrating it can be to deal with furnace issues, especially when they seem to stem from recent work. At SuperTech, we make sure to do it the super way, not the easy way!

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