Why Is My Furnace Leaking Water? A Pittsburgh Tech Answers

| Posted in:  Help Guides/Heating

Have you noticed water pooling around the base of your furnace? If so, you probably want to know why (and more importantly), how to fix it. 

The key to determining why your furnace is leaking is figuring out what kind of furnace you have: 

  1. Non-condensing (conventional) furnace
  2. Condensing (high-efficiency) furnace  

How do you know what kind of furnace you have? 

A high-efficiency furnace will usually have a white PVC pipe coming out the side or top of the unit, whereas a conventional furnace will typically have a metal flue (vent) pipe.

Below, we’ll look at why your furnace may be leaking depending on what kind of furnace you have (conventional or high-efficiency). 

Rather have a professional diagnose your furnace leak and repair it? We get it! We have spent years serving Pittsburgh homeowners and can quickly figure out where your furnace leak is coming from.

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If you have a non-condensing (conventional) furnace

There are two main reasons why your conventional furnace may be leaking: a clogged humidifier or a poorly designed flue pipe.

1. Leaking humidifier

Some furnaces have a built-in humidifier. If this humidifier is clogged or damaged, it could cause water to leak onto the floor around your furnace.

To fix a leaking furnace humidifier, your best option is to reach out to an HVAC professional. They will be able to fix the leak without causing further damage to your existing furnace. 

Not sure if you have a humidifier? It’s normally attached to the outside of your furnace and looks like:

2. Poorly installed/designed flue pipe

If you have a conventional furnace, it’s going to have a metal vent called a flue pipe. 

During the combustion process, your furnace creates gases, and a flue pipe is the pathway for those gases to safely exit your home.

But here’s the catch: Flue pipes are not always installed or designed correctly. If they are too large or aren’t sloped correctly, too much air can circulate in the pipe, trapping the gas. If the gas sits in the flue pipe for too long, it cools down, turning back into a liquid. That liquid can then run down the pipe and settle at the bottom of your furnace. 

If you have a faulty flue pipe, you’ll need to contact an HVAC professional. They can take a look at your flue pipe and determine what needs to be done to fix this issue going forward. 

If you have a condensing (high-efficiency) furnace…

You’re in luck! 

Unlike conventional furnaces, high-efficiency furnaces actually create condensation, so if you’re noticing water at the bottom of your furnace, it’s most likely a minor clog or leak.

Why do high-efficiency furnaces create condensation?

While conventional furnaces only have 1 heat exchanger, high-efficiency furnaces have 2 heat exchangers. This extra heat exchanger absorbs more heat, which lowers the temperature of the exhaust gas your furnace produces. When the gas reaches a lower temperature, it changes from its gas state to a liquid. This liquid is carried out of your home via a condensate line/drain. 

Now, if there are any clogs or leaks along this line or if the condensate pump is broken or faulty, that liquid will have nowhere else to go but onto the floor surrounding your furnace. 

To sum things up, if you do have a high-efficiency furnace and it’s leaking, it’s likely because of a:

  • Broken or faulty condensate pump
  • Leaky or clogged condensate line or drain trap

Our suggestion would be to contact an HVAC professional to come check it out. While you can unclog a drain pan on your own, there could be other issues that only a professional will be able to detect and repair.

Alternative Reason: It’s actually your AC that’s leaking

Hear us out: If your furnace leaks when your AC is on, it’s likely your AC that’s leaking, not your furnace.

Many times, the condensate drain line of your AC system sits on top of (or close to) your furnace. If this starts to leak, you’ll likely notice water pooling near the bottom of your furnace, making it seem like it’s your furnace that’s leaking.

An AC drain line can leak for the same reasons a furnace’s drain line may leak:

  • Piping issue
  • A backed-up or clogged drain 

There’s a pretty simple way to determine if it’s your AC or furnace that’s leaking. Is your AC turned on or is your furnace turned on? If it’s cooling season, it’s likely your AC that’s leaking. If it’s heating season, it’s likely your furnace.

The solution for a leaking AC system is to contact an HVAC professional. They will be able to verify whether your AC or furnace is leaking and stop it.

Still having issues with your furnace? Reach out to the Pittsburgh Pros

If your furnace is still leaking, it’s time to call in a pro. We can help with any furnace repair that your system may need.

Schedule service!