Furnace Leaking Water? Here Is the Solution

furnace leaking water

We don’t live in a perfect world free of mishaps. On the contrary, now and then, we run into problems in our homes. One such issue is water leaking from the furnace. It’s also one you want to deal with instantly. 

There are several reasons a furnace leaks water, some of which are minor while others major.

If you just found out that your furnace, an integral part of your HVAC system, is leaking water, worry not. This article helps you understand the best solutions to a furnace leaking water.

Before calling in a furnace repair person or HVAC technician, there are steps you can follow to save you money.

Read on to understand the various causes of water leaking under the furnace and the best solution to each.

Furnace Leaking Water When AC Is On

One of the reasons why your furnace may be leaking water is the Ac. This happens especially in mild climates like that in California, or during the seasonal grey period where you have to use the air conditioner and furnaces on the same day.

In such cases, water from the condensation pan may fill up and drip onto your heating system. That means the air conditioner is the issue, not the furnace.

Clogged Condensate Line

If you suspect this might be the cause of the leak, and maybe observe it always happens when the AC is on, here’s how to fix a condensation leak in the furnace. Check to see whether your air conditioning and furnace share a condensate line and drain to establish whether it’s clogged. 

If it’s the case, unclog it to solve the furnace water drain problem. If it’s not, check for other potential causes.

Water Dripping From Furnace PVC Pipe

Sometimes, water leaking underneath the furnace may be due to a condensation leak. This is usually the case when your high-efficiency furnace gets the heat from combustion gases and later cools. 

A PVC pipe should direct the resulting condensation to a drain.

If water leakage is due to high-efficiency furnace condensation problems, then the PVC pipe might have any of the following issues: 

water dripping from furnance pvc pipe

The Drain Pipe is Blocked

The additional water from condensation should drain through a pipe to the drain from the furnace. With time, this pipe may get blocked due to clogging, leaving the water with nowhere to go. A furnace drain trap full of water means the water gets back up and starts dripping from the furnace.

The solution is to unclog the blocked part of the pipe to allow the water to drain without moving backward. In fact, it’s advisable to inspect your pipes regularly and clean them to avoid this kind of problem.

The Pipe is Broken

A broken PVC pipe may also result in water leaking underneath the surface of the furnace. Inspect the pipe thoroughly for any signs of cracking that may be causing the leakage.

If you identify a broken pipe, repair it immediately. If it has been there for a while, you might consider replacing it with a new one.

The Humidifier is Leaking

Most homeowners opt to incorporate a humidifier in their heating systems to make their living spaces more comfortable during the dry winter season. The device adds moisture to the air as water from the plumbing system constantly moves through it.

But did you know that your humidifier may be the reason your furnace is leaking water? It happens if there’s a clog or breakage in the humidifier. This issue often presents itself as the furnace leaking water while, in the real sense, it’s the furnace humidifier leaking.

Again, you have to eliminate the clog or repair the breakage to ensure a smooth flow of water through the humidifier, subsequently stopping the furnace from leaking water.

Heat Exchanger Leaking Water

Problems with your furnace’s heat exchanger could also cause a water leak. Unfortunately, a heat exchanger leaking water is one of the most expensive problems to repair. Therefore, it’s an issue you want to avoid as much as possible.

After checking for all the other potential causes to no avail, then it’s likely the heat exchanger causing the leak. And if the water leak is coming from it, you need to repair this component. In fact, it calls for the replacement of the whole furnace.

Seek help from an HVAC technician or repair person who will inspect the furnace for this issue. If they deem it right to replace the furnace, then act accordingly.

Heat Exchanger Leaking Water

Furnace Leaking Water in Summer

During summertime, chances are you don’t use your furnace for heat. You probably only use it for the blower fan. 

If you notice your furnace leaking water during summer, then it means something may not be functioning well. The most likely causes for the furnace leaking water are:

  • Filter clog: If the filter is clogged, it reduces airflow through your coil. At first, this causes the coil to freeze, but a blocked filter sooner or later causes airflow restriction, leading to water leaking.
  • PVC drain line clog: The longer your systems have been around, the more dirt and dust they collect on the evaporator coil. Eventually, these fall into the drain line and plug it. As a result of this restriction, water moves back towards the coil and fills up, ultimately leaking onto the floor.
  • A leak in the drain pan: Sometimes, the pan may rust, subsequently developing holes that leak water. This usually happens if water has rested on the pan for too long.
  • Condensate pump problems: A home with a condensate pump means you have an extra electrical component that can fail. This may also result in the furnace condensate pump leaking.

Solutions to Furnace Leaking Water in Summer

Follow these steps to remedy the problem of your furnace leaking water in summer:

  • Go to the shutoff switch located next to the coil and furnace and shut the system off. If you cannot find the switch, just turn off the system at the breaker.
  • Clean the sitting water quickly to avoid damaging whatever component it’s in contact with.
  • Check the filter to ensure the water leak has no impact on airflow through it.
  • Place a water-safe vacuum around your PVC drain line to remove potential clogs, blocks, and any other debris. Later, you can turn the AC system on and check whether you have solved the leaking problem.
  • Pour water into your condensate pump and see whether it reacts. If it does pump the water, then it means the drain line is clear. On the other hand, if it fails to respond, there must be a mechanical problem somewhere. You need to call in a professional.

Water Under Furnace in Winter

In most cases, the furnace leaking water in winter is due to humidifier problems. 

The humidifier is installed into the plumbing system and connected to the furnace. The equipment has water constantly moving through it, helping add moisture to air in your home to make it more comfortable.

If the humidifier gets clogged or broken, water will start dripping. That’s why you will notice water under the furnace. So, it’s the humidifier leaking, not the furnace.

Follow the steps mentioned above when you notice the leak, only this time it’s the humidifier you will check for clogs or breakage. If it’s the case, you will have to purchase a new one and install it. 

The great news is this doesn’t necessarily require you to hire a professional if you have already identified the cause of the leak and can repair it yourself.

Is Furnace Leaking Water Dangerous?

Furnace leaking water can be dangerous. That’s why it’s advisable to act fast. However, the issue may not be due to the furnace itself but other components surrounding or connected to it.

Once you identify a leak, inspect your furnace immediately to establish the cause of the problem. If you happen to know the cause of the leak, find a solution promptly, and if necessary, call in a furnace repair person or technician to diagnose, service your furnace right away, and furnish you with the furnace leaking water repair cost.

furnace leaking water dangerous

When to Call a Furnace Repairman

As mentioned earlier, the first thing to do once you identify a furnace leaking water is to inspect it to try and identify the issue. This is often easy, especially for a carrier furnace leaking water. But if you cannot tell where the leak is coming from, contact a licensed furnace technician.

Water leaking is an issue that needs dealing with without delay. Therefore, shut off the system immediately as you wait for the technician’s arrival. 

It’s essential to hire a reputable technician with a track record of serving customers satisfactorily. That way, you’re guaranteed the water leak problem is solved once and for all.


While furnace water leaks can happen to anyone and due to many reasons, they are avoidable. Change your furnace filter from time to time—say every three months, and maintain your furnace. It’s also a good idea to have a licensed technician inspect it at least annually. That way, if there are any issues, you can identify and correct them in advance.

But if you’re in a situation where the water leak has already occurred, you know what to do. Identify the leak, the solutions available to you, and correct the issue by following the necessary steps.