As your gas furnace runs, is there water leaking at the base? Is the furnace's air filter wet, too? There are a few things that could be happening here. But if you have a high-efficiency furnace, here's the most common cause: a condensation leak. We'll explain why a furnace creates condensation, and what's causing it to leak out of your furnace. Note: You'll know if you have a high-efficiency furnace if:

  • The yellow energy guide tag says your furnace's efficiency is 90% or higher AFUE.
  • The vent/flue pipe is white PVC as opposed to metal.

Why a high-efficiency furnace creates condensation

How in the heck does a high efficiency furnace create condensation/water anyway? It's all about how the furnace extracts heat from combustion gases. A lower-efficiency furnace extracts some heat from combustion gases and then quickly vents them out the flue pipe. But a high-efficiency furnace, to extract more heat, has 2 heat exchangers. These allow the furnace to extract heat from the gases for a longer period of time. This causes the combustion gases to cool and then condense. That condensation then exits out your home through a drain. But if that water is pooling around the furnace, there's a problem preventing it from draining properly. Causes of a condensation leak around a high-efficiency furnace

  • Clogged condensation tubing
  • Clogged condensation drain
  • Breaks in the condensation line
  • Issues with the condensate pump (if you have one)

You'll need a furnace technician to diagnose which of these is the issue and then fix it.

Other causes of leaking water around a furnace

If you have a conventional, standard-efficiency furnace

Then its flue pipe may be incorrectly sized.

If you have a whole-house humidifier connected to the furnace

There may be an issue which is causing the humidifier to leak into your furnace. Your humidifier should be getting annual maintenance from a professional to prevent this.

Need professional help in the Atlanta area?

Ragsdale Heating, Air and Plumbing has been serving the Atlanta area for 20 years and can diagnose and repair your furnace's leak issue.

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