Why Is My Furnace Leaking Water? Let’s Figure It Out

For the most part, home furnaces will stay dry and require minimal maintenance and upkeep. But what if you find a water leak in your furnace? What should you do and what might be the cause of your leak? The answer to this question will depend on a few different factors, this includes the type of furnace you have.

However, in most cases, your furnace will leak water because of a condensation leak. When the pipes found in high-efficiency furnaces are clogged or broken condensation will build, and a leak will occur. There are other reasons that a leak could happen, but this is the main reason a furnace will leak. 

Still, regardless of why your furnace is leaking, you need to contact a professional right away. Furnace leaks will not resolve themselves, and the longer you wait to fix this issue, the more damage the leak could cause. (Related: Are High-Efficiency Furnaces Worth The Money?) Water can create mold buildup and other issues in your home. So, we highly recommend getting your leak fixed!

We’ll talk more about what causes furnace leaks and how you can handle this situation throughout the rest of this post, so keep reading.

Why is your Furnace Leaking Water?


Condensation Leak


As we talked about before, a condensation leak will be the most likely cause of a furnace leak.  However, it’s important to note that high-efficiency furnaces usually have this problem. Because of the heat and gas exchange that occurs in these types of furnaces, condensation needs to be drained out of the furnace.

Standard efficiency furnaces don’t produce condensation because gas is quickly vented from the furnace; so they don’t typically have condensation leaks. On the other hand, high-efficiency furnaces need pipes to get rid of this condensation that forms from high levels of heat. Floor drains are also installed into this type of furnace. However, if either one of the draining pipes in your system gets clogged or breaks down then the condensation created by your furnace will start to leak. You will notice a big puddle of water forming around the furnace base.

Finally, if you do have a condensation leak with a standard furnace, there could be a sizing issue with your exhaust pipe or flue pipe. This is unlikely, but make sure to call in a professional to assess your system.

Your Humidifier is Leaking


A humidifier leak can also cause water issues to form with any type of furnace system. Especially if these two systems are set up together, you can have major problems with leaks if your humidifier starts to break down or clog.

Humidifiers help to get rid of moisture in the air, but if the drain line is not working or is blocked, then excess water can leak into your furnace and cause water dripping. 

You have a Plumbing Leak


As you already know, furnace leaks can happen for many different reasons. In fact, other home systems can affect your furnace and create water leakage. So, your furnace might not be causing the leak, it could even be caused by your plumbing system.

This is like a humidifier leak, as excess water from your plumbing system can leak into your furnace pipes and cause water to start dripping. Usually, this means that your plumbing system will need to be repaired because of clogging or leaks.

You have a Clogged Filter


Furnace filters need to be replaced and even cleaned to keep them functional. If you don’t clean or replace them, then your filters will get clogged, and this will make it much harder for air to flow within your furnace system.

This might not seem like a big deal, but when there is less airflow, the coils in your furnace can start to freeze up. Your frozen coils can start to melt, and this will create a water leak around your furnace system.

Your Air Conditioner is Leaking


This might seem like an unlikely cause of a furnace leak, but your air conditioner can create problems for your furnace, especially if they are used together. Some more mild climate areas are especially susceptible to this problem.

When using both these systems together to cool and heat your home within the same season, you will get some major condensation. In particular, your air conditioner can start to form more condensation and will leak. The leaking water in your AC can enter your furnace system and create puddles of water around your furnace, especially if both systems share the same drain line.

Your Heat Exchanger Is Broken


Finally, a broken heat exchanger could be causing your furnace to leak water. If your heat exchanger is broken, then water will start to drip from your furnace. Really, this is the worst-case scenario, as the repairs for this type of damage can be pricey.

We recommend looking over your system fully and considering the other causes we have talked about before you get your heat exchanger repaired. It’s better to rule out all the possible reasons your furnace is leaking first. Then, if there is no other explanation, have someone look at your furnace and repair it.

In some cases, you might even have to replace your furnace unit entirely if the damage is bad enough. But make sure to get an expert opinion before you replace anything.

What Should you do when your Furnace is Leaking Water?


You might be wondering what you should do if you have a furnace leak. We’ll go over this briefly in the final section of the post.

  1. 1
    First, you want to act quickly to get your leak fixed. Water damage is no joke, and the longer you let your furnace leak, the more money you will have to pay for repairs. So, call in a professional as soon as you can!
  2. 2
    After you have done this, you need to turn off your furnace. You don’t want more water to drip, so your system needs to be fully shut off until someone can repair it for you.
  3. 3
    Once your system is shut off properly, you can clean up the water near your furnace to prevent any further water damage.
  4. 4
    Finally, we recommend checking your air filter. Your furnace could be leaking because your filter needs to be replaced or cleaned. So, check this area of your system, as this is a relatively easy fix.
Kenneth Wilson
September 18, 2021
Contractor Tips, HVAC

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done.