Furnace Leaking Water? (Possible Causes & Fixes)

Heather Robbins
by Heather Robbins

As you’re used to your furnace doing its job without any issues, it can come as a shock to see water pooling around its base and realizing that something is wrong. It’s essential to take immediate action as, left uncorrected, even a small leak can result in extensive and costly damage.

There is a whole range of reasons why a furnace can leak—these range from simple issues, suitable for an easy DIY fix. Or you may have more severe problems, which requires a professional HVAC specialist’s intervention. Causes include:

  • Plumbing issues
  • AC issues
  • Blocked filters and vents
  • Heat exchanger

In this guide, we’ll run through the most typical causes of furnace leaks, explain what to do when you first spot a leak, and consider the cost of DIY and professional repairs. We hope this will help you deal with any furnace leak in the safest, most appropriate, and cost-effective manner.

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Possible Issues Of A Leaky Furnace

Your furnace leaking isn’t always an end-all situation. Sure, it’s frustrating as many issues can cause this to happen. It’s a good idea to work through each of the following possibilities to get a good idea of what may be wrong. However, if you can’t find the leak’s source, it’s an even better idea to call a professional to help you as a leaky furnace is something you need to fix right away.

Plumbing Is Leaking

Finding your furnace leaking water may mean there’s an issue with the plumbing and not the furnace itself. There actually may not be an issue with the furnace’s components, which is a good thing. However, the leak still needs to be addressed.

When a clogged or broken plumbing pipe causes a backup in the drainage system, it seems as though the furnace is leaking. These pipes need to be repaired or replaced. If you repair or replace the pipes and the leak is still happening, you may need to take a closer look at the furnace itself.

Clogged Or Broken Humidifier

Another reason for your furnace leaking water is a break or clog in the humidifier. These devices are hooked up to your plumbing system to add moisture to the air. If any breakage occurs, or they get blocked, water will start dripping around the furnace.

A clogged or broken humidifier is a relatively easy fix. If it’s clogged, you can clean it out. If it’s broken, then of course you’ll have to replace it, but after doing so, the leak will stop, and your furnace will be as good as new!

Heat Exchanger Problem

A problem with the heat exchanger in your furnace could cause a water leak and, unfortunately, is one of the most expensive repairs. If you’ve looked into the other possible causes of a leak and can’t find it, it may be the heat exchanger. A new unit may need to be installed.

A technician will be able to advise you on whether this needs to happen. In this situation, it would be a good idea to call a professional to get it checked. This way, you can bypass any unnecessary costs in the long run.

Leaky Air Conditioner

In mild climates like California, furnaces and air conditioners are sometimes used during the same season. When this happens, and your air conditioner is being used, the condensation pan fills, and water drips onto the heating system. This makes it seem like you have a furnace leaking water, but it’s actually the air conditioner.

Filter is Clogged

If your furnace’s filter is dirty and clogged, it will restrict airflow through the furnace coil. Many times this causes the coil to freeze. However, sometimes it causes water to leak and pool up around the furnace. Make sure you always check the condition of your furnace’s air filter and replace it if it’s dirty.

Condensation Leak

This is one of the most common reasons for a furnace leak. Many furnaces run at high efficiency, which means it has an AFUE rating of either 90 or above. This type of furnace contains two heat exchangers that help it produce more heat.

Condensation caused by the production of heat must get carried out of your home via the pipes. Most of the time, this is through a floor drain. When these pipes either get clogged or break, you’ll get leaking condensation around the base of the furnace. Once the water starts to collect and pool up, there’s a potential for water damage.

Frozen Coil

If your evaporator coil gets too cold, it can cause the moisture collected on the coils to freeze. When the ice eventually melts, the drain pan can overflow, causing water to gather around your air handler. In addition to possible water leaks, a frozen evaporator coil also raises your energy bills and reduces your AC system’s performance.

What Causes Your Evaporator Coil To Freeze?

The most common causes of a frozen evaporator include:

  • A dirty air filter: A filthy air filter blocks warm air from entering your AC system. If the evaporator coil can’t get enough warm air blowing over it, it will freeze.
  • Closed/blocked air vents: Similar to a dirty air filter, closed/blocked air vents restrict airflow into your system, which could cause the evaporator coil to freeze.
  • Refrigerant leak: Your evaporator coil uses refrigerant to remove heat from the warm air. If refrigerant levels drop too low, the coils will get cold and start to freeze. If you have low refrigerant levels, this means there’s a leak somewhere in your system. Since refrigerant is a potentially harmful substance, only a professional should find and repair any refrigerant leaks.

Faulty Condensate Pump

High-efficiency condensing furnaces typically drain down. But if the water has to go up and out of a basement or crawlspace, a pump is required.

First, check the drain; if it is clear and doesn’t have a humidifier, then the pump is likely the cause. Experienced DIYers with mechanical skills that enjoy tackling new projects can probably repair or replace the condensate pump. They’re easier to replace than repair.

Vent Leaks

High-efficiency furnaces usually have white PVC vent pipes, whereas conventional furnaces have a metal exhaust vent pipe. All the gases produced during combustion are carried through the exhaust vents and released outdoors when they are hot.

An incorrect sized pipe for your furnace will cause these gases to get trapped inside due to extra air. This will lead to the gases cooling down and condensation taking place that can leak out of your furnace in the form of water.

First Steps To Take When You Notice A Water Leak

As soon as you notice water standing around your furnace’s base, it’s essential to take immediate action. Take a few steps before calling a professional to come and advise you on where the problem originated.

Step 1: Shut Down The System

Close down the entire system. The switch will be situated on the unit itself, or next to it. If you’re unable to locate it, turn the furnace off at the breaker.

Step 2: Remove The Standing Water

Clean up all the water that is now standing around the base. Damage can happen rapidly, so be sure that the area is thoroughly dry. If there is too much to remove with cloths, you may need to use a wet/dry cleaner. These can be rented daily from a local DIY or hardware store.

Step 3: Check The Air Filter

It may be that the issue is something as simple as a clogged air filter. If this is the case, remove and replace the air filter. Or, if you see that it’s dirty, clean it with an air compressor and insert it into your furnace. You can then run your furnace for 24 hours, and if you notice on water leaks, then you’ve fixed the issue.

Step 4: Locate The Source Of The Leak

If none of the above steps have stopped your leak, it may be time to call a professional to get a diagnosis so that you don’t pay for parts that you don’t need. Hiring a professional doesn’t necessarily mean you have to pay them to fix the issue. It just helps you to find out what the problem is, so you know what you need to buy as far as parts go.

If you can see exactly where the leak originates, this will be useful when contacting a professional. When you decide to seek professional help, ensure that you source a reputable company. They should have experience working with furnaces and AC units.

How much Does It Cost To Repair A Leaking Furnace?

Cost To Repair Furnace





Heat Exchanger/Blower Motor

$1,800 – $2,900

Average Repair Price


Neglecting to diagnose the reason for your furnace leak, or taking action to fix it promptly, can have expensive consequences. Nationally, the average cost of calling a professional to change a filter is around $85.

However, if a heat exchanger or blower motor needs to be replaced, this rises to as much as $2,900. The average cost of a professional repair is around $425.

Cost To Replace A Furnace

Cost To Replace Furnace



Installation Fee


Standard Tank Storage Unit

$400 – $1,600

$150 – $600

$550 – $2,200


$250 – $2,500

$400 – $1,500

$650 – $4,000

High Efficiency

$700 – $3.000

$150 – $600

$850 – $3,600


$1,000 – $6,000

$2,000 – $4.000

$3,000 – $10,000

Standard Tank Storage Unit

The average price of a standard tank storage unit ranges between $400 and $1,600, with an additional $150-$600 installation cost. Should you go for a tankless model, costs can start at around $250 and climb as high as $2,500, with an extra $400 and $1,500 for installation.

High-Efficiency Furnace

If you decide to invest in a hybrid/high-efficiency furnace, prices currently range between $700 and $3,000. The installation of a high-efficiency furnace will cost between $150 and $600.

Solar Unit

A solar unit can cost anything from $1,000 to $6,000, and expect to pay from $2,000 and $4,000 for the installation.

However, although the investment in the last two options is greater, you can choose to offset the higher costs of hybrid/high efficiency and solar furnaces against the savings you’ll make on utility costs, especially when you calculate these over 5-10 years.

When You Should Hire A Professional

It’s a good idea to hire a professional when you cannot find the source of the leak yourself. This does not necessarily mean you will pay them to make the repairs, but you will pay for the diagnosis.

Some professionals offer a free consultation, while others will ask for a $50 to $100 fee. However, it may be better to pay this amount rather than throw hundreds of dollars down the drain for parts that you do not need.

Does Homeowner’s Insurance Cover Furnace Replacement?

Homeowners’ insurance varies depending on the state and the company you choose. Typically they won’t cover systems that break due to age or normal wear and tear. You may be covered if the furnace breaks due to fire or natural disaster, in which case you may be covered for the cost of repair or replacement.

Although your homeowner’s insurance probably won’t cover your furnace, it will probably cover damage caused by a malfunction. For example, if water from the furnace damaged flooring, or even if it resulted in injury, you would probably be covered for these liabilities. Therefore, it’s essential to check your homeowner’s policy carefully.

Related Questions

Is a leaky furnace dangerous?

A leaky furnace isn’t typically dangerous, though, it will cause significant repair costs if left without unattended. Sometimes, your furnace can leak carbon monoxide, although your sealed furnace flue should safely vent the carbon monoxide to the outside.If you begin to feel tired, sick to your stomach, or like you aren’t yourself, you may have a carbon monoxide problem. It would be a good idea regardless to stick a carbon monoxide detector near your furnace.

How long do furnaces last?

The average lifespan of a gas furnace is around 15 years. However, this varies significantly depending on the brand, the model, how heavily it is used, and whether it is correctly maintained.

How do I know if my condensate pipe is clogged?

A clog in your condensate pipe will present certain signs such as:

Do You Need a Furnace Repair Contractor?

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Our Takeaway

Taking care of a leaky furnace should be your first order of business upon finding an issue. Doing so will help to avoid more expensive repairs down the line. The longer you let a leak sit, the higher risk you are at for more costly repairs including water damage.

It’s also a great idea to call an HVAC technician even if it’s just for a diagnosis. That way, it will give you a general direction to aim when it comes to repairing your furnace yourself.

Heather Robbins
Heather Robbins

Heather is a passionate writer who loves anything DIY. Growing up, she learned everything from home repairs to design, and wants to share her tips with you. When she's not writing, she's usually hiking or searching for her next DIY project.

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