Why is Water Leaking from the Furnace?

Why is Water Leaking from the Furnace?

leaking furnace

Soon, the temperatures will be turning cooler and we’ll be counting on our furnace to keep our homes warm and comfortable. One of the more common questions that we hear about is, “why is water leaking from my furnace?”

Don’t worry, we’re here to help you troubleshoot. And, our techs here at Airforce Heating & Cooling are always ready to help!

Here’s the first thing we need to determine:

Is your furnace a high-efficiency condensing furnace or a conventional furnace? This requires that you take a look at your furnace and determine the following:

  • If you see a white PVC vent pipe coming out of the side or top of your furnace, you most likely have a high-efficiency condensing furnace.
  • If you see a metal vent pipe instead, you have a conventional furnace.

Now, let’s move on to the potential causes of this puddle of water:


Leakage could very well be the result of the condensation tubing becoming clogged or from breaks in the line. Many of today’s high efficiency furnaces, meaning it has an Annual Fuel Utilization Efficiency (AFUE) rating of 90% or higher, produce condensation.

Condensation is typically drained through a floor drain. However, if the tubing responsible for this is clogged or broken, it may result in a leak. Additionally, the floor drain itself could be clogged.

High-efficiency furnaces create water because they have two heat exchangers, one more than a conventional furnace. The two heat exchangers absorb so much heat that the exhaust gas changes from a gas state to a liquid state. Condensation forms and then drains out through the condensate line.

Your furnace must be professionally serviced so it can properly drain the water that condensates. If there’s any leak or clog, the condensation can’t be carried out of your home and ends up pooling around your furnace.

If you have a standard-efficiency furnace, there should be no condensation.

Humidifier Leak

Along with the furnace comes the central humidifier, which can also be a source for leaks. Humidifiers need water to create humidity, so water is constantly flowing into and out of it as the humidifier adds moisture to your home’s air.

A humidifier leak is something that would typically be caught early on though – if you get routine maintenance. If you haven’t had a tune-up for your furnace, this might be your issue. If it is your humidifier, address this right away as it can do a lot of internal damage to the unit.

Secondary Heat Exchanger

Another possible cause is an issue with the secondary heat exchanger. Unfortunately, this type of problem might be an expensive fix or might require that you replace your furnace.

Clogged Internal Drain

Last but not least, you could be dealing with an internal drain system that is plugged. This happens if your AC unit is still running and shares this drain with the furnace. This could potentially cause a clogged drain.

The bottom line is that leaks can cause problems for your home, such as damaging floors and walls or leading to mold growth. The best way to identify the right solution is to have a HVAC professional diagnose the issue and offer solutions to the problem.

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