Furnace Leaking Water When Heat Is On – What To Do?

If you have ever experienced your furnace leaking water when the heat is on, then your heater might be faulty and need repair. We talked with HVAC experts, and here's what they listed as the cause of this problem and how to fix it. 

A clogged furnace drain usually causes the furnace leaking water when heat is on; in this situation, the best you can do is to unclog it. If that's not where the problem is coming from, then it might be other parts being clogged, including the condensate drain and condensate pump. A faulty humidifier or heat exchanger can also cause your furnace to leak.

There are still a few reasons you should know about. Most importantly, the remedies will also be discussed in this article. So hang on and keep reading. 

A home high efficiency furnace, Furnace Leaking Water When Heat Is On - What To Do?

The Furnace: An Essential Home Heating/Cooling Appliance 

A furnace is a piece of home equipment that distributes heat around the home. They help to maintain the cold temperature of the home during winter. Most homes use a furnace as the heat provider instead of other heat systems. 

A person changing an air filter on a high efficiency furnace

There are also several types of furnaces, each unique in its own way. The electric furnace, which is the most popular, can help you turn electric energy into heat energy around the home. The oil or gas-fired furnaces convert mechanical energy from fuels into heat energy. 

The furnace also comes with a thermostat that can be used to regulate the amount of heat being distributed around the home. Furnaces, just like most home appliances, develop faults sometimes. If your furnace starts to leak water, then here are a few things you should know. 

Reasons the Furnace is Leaking Water

Heat systems around the home, AC, furnace, or others undergo a certain downtime stage. If it is a water leak, here are the common reasons. 

Humidifier Leak

The humidifier usually comes with a furnace. However, once it starts leaking, it becomes a problem for the furnace too. When the humidifier is cracked or clogged, a leak is expected to happen, and water can escape through the hole.

Plumbing Leak

If the humidifier is not leaking, then you should probably check parts of the plumbing system. In fact, nothing might be wrong with your furnace; the plumbing system leaking means the issue comes from the pipes, zinc, and hoses. 

Clogged Filter

Senior caucasian man changing a folded dirty air filter in the HVAC furnace system

One of the reasons manufacturers advise you to clean your furnace is to prevent situations like this. Once the filter is too dirty or clogged, it would restrict airflow in the furnace. This would lead to freezing in other systems, and water might start leaking out of one of the furnace systems.

Leaking AC Unit

Water leaking from the air conditioner drips from the cooler

You use an AC and a furnace together in your home. If anything should go wrong with the AC and it starts leaking water from its pan, the furnace might be suspected to be the source of the leak, but it might be the AC. After inspecting your furnace, always check your AC to make sure water isn't leaking from any area. 

Condensate Leak

The fact that furnace systems release warm air means there is an opposite reaction. An instance might be water condensing in the furnace when it's working. Although the water gets to leave through a pipe, if there is an issue with the pipe, then water can form in an area without passing out. 

If you are able to find out where the actual problem is coming from, you are halfway solving the problem even by yourself. Check out ways to stop your furnace from leaking water below.

How to Stop Furnace From Leaking Water

According to HVAC professionals, there are a few first-hand measures you should try first for any furnace that is leaking in your home.

First, turn off the furnace and clean up all the water on the floor. This will help to reduce the water being lost in it. If after turning it off (whether from the thermostat or its normal switch) you still notice water drops or leaking, then the problem might not even be from the furnace. 

Remove the front panel of the furnace so that you can have access to any of the parts that have water around it. After which, you can screw back the panel in the meantime and get help from a professional. 

How to Stop Furnace From Leaking Water When Heat is On

Replace and clean the hepa filter

As explained earlier, you need to identify the problem causing the furnace to leak before you can point out the best solution. Below are the reasons your furnace leaks water when heat is on and how to stop them:

Unclog The Condensate Drain 

All the water that condenses in your furnace is passed out of the system via a condensate drain. Once it accumulates dust or dirt, it becomes clogged. So, the best you can do is to unclog it so that the condensate can leave the furnace easily. 

Troubleshooting The Condensate Pump

Another problem you should look out for first is if your condensate pump has an issue. Mostly, it can be easily fixed, but if need be, you should replace it or take it to an HVAC technician.

Repair The Humidifier

The problem might be from the humidifier instead of the furnace directly. It is better to call an HVAC expert at this point, especially if the humidifier is not blocked but broken Instead. 

Repair the Heat Exchanger

The heat exchanger might be broken or cracked which might be causing leaking water. This might even be a more severe problem because a bad heat exchanger releases toxic chemicals which are dangerous to your health when you inhale them. 

How Do You Unclog a Furnace Drain? 

The drain in a furnace helps to pass out the by-product of the process occurring in the furnace, which is water. When it becomes clogged, water will continue to remain in your furnace, and a leak will arise from this soon. 

Even though you shouldn't be worried at this point, the water would spill to the floor if managing condensation becomes too hard for the furnace.

If you want to get it unclogged though, you can use a wet or dry vacuum to spin out the dirt and sediments in the pan. Also, you can open the drain pan and use running water at its highest pressure to wash off the clogged drain pan.

How Do You Unclog a Condensate Drain Line? 

Simple, once the condensate drain line has been clogged with dirt, then you should also expect water to drip off the condensate drain line. 

So, just like with the furnace drain, you can also use a vacuum to suck out the dirt and debris. Rinsing with water might be another easy way to solve the problem. Also, if you can poke a wire along the drain line, you can use it to draw out all the dirt and slime in it.  

How Much Does it Cost to Unclog an AC Drain Line? 

The price depends on both the utility of labor and the area you live. However, there is still a range at which any HVAC professionals will charge you for unclogging the AC drain line. Somehow, you would have to spend about $75 to $250 to get your air conditioner drain line unclogged.

Is Bleach or Vinegar Better For AC Drain Line? 

Top view two bottles white vinegar and bottle of apple cider vinegar

Vinegar is safer than bleach when it comes to cleaning the AC drain line. Bleach contains heavy chemicals which can be harmful to your air conditioning system and not only to the drain. In fact, it might cause a lot of damage when it starts to affect the copper tubes.

You can use vinegar to clean an AC drain line with the following steps:

  1. Switch off the AC and disconnect it from any other electronic devices.
  2. Locate the drain line first which is a white T-Shaped tube, and remove its plastic cap.
  3. Pour a cup of diluted vinegar into the AC drain line. After 30 minutes, turn on your AC drain line again.


Leaking issues from your furnace can be avoided permanently as long as you carry out regular routine appliance checks. Unfortunately, damage to your furnacescan still happen. Since you are aware of the reasons and the solutions, too, as explained in this post, you can easily fix your furnace and get it functioning properly again. 

For more furnace-related articles, check out these engaging posts: 

Furnace Blowing Cold Air Only at Night - What to Do? 

How to Clean an Electric Furnace

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