How To Fix It

Why Furnace is Leaking Water?

A furnace does not require water to operate. So, finding out that your unit is leaking might take you by surprise.

A high-efficiency furnace will develop a leak if something is wrong with its draining system. Conventional furnaces rarely leak, so you might want to check the AC, humidifier, or water heater. In some gas furnaces, a corroded heat exchanger or a poorly designed vent pipe can become the source of the problem. 

Keep on reading to find out if a furnace leaking water is an emergency and how to prevent the leak from happening in the first place. 

Why Furnace Leaking Water?

If you are a proud owner of a high-efficiency furnace, then it will be producing water during operation, and if there is a leak, then it looks like there is something wrong with the condensate drain or the condensate pump.

If you have a regular, conventional furnace, then it won’t be generating any water while running. If you find water around the unit, then it might be coming from another appliance. For example, your air conditioner or the water heater.

Read: How To Reset Lennox Furnace?

Why Is My Furnace Leaking Water from the Bottom?

If it’s the actual furnace that’s leaking, then it might be because the condensation is not able to drain properly. You may have to deal with one of the following issues:

A leaking condensate drain hose

The drain hose is the pipe that slopes down from the exhaust pipe. It can get clogged with debris, disconnected, or damaged.

A leaking inducer assembly

After the condensate drain, the condensation travels through the inducer assembly (that’s a small fan that pulls the air through the heat exchanger). The water will start leaking out of the unit if the assembly has a hole or a crack in it. 

A leaking condensate drain line

Once the condensation gets through the inducer assembly, it ends up in the drain line. If this element has a hole in it or is not connected properly, water will appear under the furnace. 

By the way, if the drain line is very dirty or clogged, the built-up condensation might go back up the line. This, in its turn, can create a leak as well.

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Read: How To Troubleshoot And Reset Furnace?

Carrier Furnace Leaking Water

The four most common reasons for a Carrier furnace leak include:

  1. A poorly fitted drain pipe – when there’s an issue with the fitting, the condensate can get pushed back into the condensate line. In such a case, the water will be leaking either from the condensate assembly or from the actual furnace (if it gets pushed even farther back).
  2. A leaking humidifier – your Carrier furnace can have a humidifier connected to it. If the humidifier is not able to drain the moisture properly, it might start dripping on the furnace.
  3. A worn-out rubber coupling – the condensate drain system has a special rubber seal that helps make sure that all the pipes fit tightly onto the furnace’s other components. Over time, the rubber coupling can thin out and crack.
  4. A corroded heat exchanger – if you have an older Carrier furnace, you should check the heat exchanger if there is ever a leak. The component can get corroded and start leaking combustion gases into the ducts; the gases will then accumulate in the ductwork and furnace and will end up increasing condensation. 

Gas Furnace Leaking Water

Even though conventional gas furnaces do not produce water under normal circumstances, this can happen in extremely rare cases, if the vent pipe has been improperly fitted or poorly designed

If that’s the issue, then the combustion gases will be staying in the system for way too long (instead of immediately leaving the house). The exhaust gases will have enough time to cool down and this will lead to the creation of condensation.

So, if your vent pipe does not have a slope to it or you have noticed that water is leaking from the actual pipe, then it looks like the element is poorly fitted. 

Read: How To Reset Furnace Control Board?

Furnace Leaking Water with AC On

In some cases, the water that you have discovered around your furnace is actually coming from another appliance. If you have a combined heating and cooling system, then the AC might be to blame.

Your air conditioner can start leaking water due to one of the following reasons:

  • A damaged drain pan
  • A frozen evaporator coil
  • A clogged drain line
  • A failed condensate pump

What Can Cause Furnace to Leak?

A conventional furnace (a unit with standard efficiency) cannot produce water during operation. However, high-efficiency furnaces do produce condensation while running.

In such units, after the combustion gases exit the first heat exchanger, they travel to the second heat exchanger. This is where even more heat gets released into the system as the vapor turns into liquid.

Of course, the water needs to go somewhere. Typically, it gets drained into a condensation pump or a floor drain.

If your high-efficiency furnace is leaking, the water is most likely coming from one of the parts of the system that are responsible for getting rid of the condensate (the drain line, the condensate trap, the condensate pump).

Read: Should You Repair Or Replace A Furnace?

Why Is There Water in My Furnace in the Winter?

If you have ever experienced any water-related issues with your furnace, the chances are high that it happened in the winter, as this is exactly when the unit gets used the most.

Before ending up on the floor, in the majority of cases, the water will get accumulated in the furnace. This might happen if you have a clogged condensation pipe, for example.

How to Stop Furnace from Leaking?

The main thing that any homeowner can do to stop the appliance from leaking is turn the system off. Ideally, you would want to shut it down at the breaker.

After that, clean up the water under the furnace and inside the unit, change the air filter (if it’s dirty), and call an HVAC technician.

If you’re an experienced DIYer, you can attempt to unclog the condensate drain

Read: What Are Common Furnace Repair Problems?

How Do You Unclog a Condensate Drain?

If there is water in the condensate pan (it’s usually located right under the indoor air handler), then your drain line is clogged.

Before tackling the condensate drain, you have to make sure that the power to the unit is turned off.

Can a Clogged Filter Cause Furnace to Leak Water?

A dirty filter can cause a leak only if you have central air conditioning and your heating unit includes an evaporator coil.

In such a case, the clogged filter will restrict airflow through the system which, in its turn, can lead to the formation of ice on the coil. When the system is not running, the evaporator coil will warm up causing the ice to thaw. 

Dirty hvac filters

How Much Does It Cost to Fix a Leaking Furnace?

It will depend on the root cause of the problem. If the leak was caused by a clog in the condensate drain, then you might end up paying $80. 

If the issue is a more serious one, then the total cost might be between $800 and $1,500 (that is if some furnace components would have to be replaced). 

Is Furnace Leaking Water Dangerous?

Typically, a leak coming from your furnace can only cause discomfort. If it is not treated in time, you might have to deal with the consequences of water damage.

In extremely rare cases, water leaking from your furnace can pose the risk of electrocution. If you have wires or electric appliances close to the unit, then you should shut the furnace down and get rid of the leak straight off.


If you have a high-efficiency furnace, it might start leaking water, if there is something wrong with its draining system. 

Conventional furnaces don’t usually develop leaks – if you see water under such a unit, then the chances are high that the AC, humidifier, or water heater is to blame.