Why Is My Furnace Leaking Water?

October 2024 · 5 minute read

A puddle of water around your furnace can be an alarming discovery. Alexander Siv of Amherst Plumbing and Heating deals with this issue often in his line of work.

“If your furnace is leaking water, you should have a technician come out,” he says. “It might be no big deal, but you’ll want to make sure.”

Read on to learn more from Siv and Joshua Smith from Berkshire Heating and Air Conditioning about reasons why your furnace could be leaking water, if it’s an emergency, and when to call a pro.

Why Does a Furnace Leak Water?

Often, there’s problem with condensation removal. This will only be found on newer, condensing forced-air furnaces with a 90% or higher efficiency rating.

High efficiency furnaces condense exhaust fumes before sending them out the flue pipe. This process creates condensation (or condensate as it’s known in the HVAC industry), which collects before being pumped into a drain. Any problem with the condensate removal hardware will cause a breakdown, and you may find water on the floor near your furnace.

Otherwise, here are the most common reasons why a furnace leaks water:

Is Furnace Leaking Water an Emergency?

It depends.

A small puddle on your concrete basement floor is not an emergency, but should be promptly addressed. “If you see water, it’s best to get it looked at,” Smith says. Furnaces have circuit boards, control boards and electronic motors. Leaking water could short something out and create an even bigger issue.

“It’s a more urgent matter in a finished basement,” Siv says. Seeping water can quickly ruin carpeting and drywall, so it’s best to fix this sooner than later.

Can a Leaky Furnace Make You Sick?

Yes.

The water leaking from a furnace isn’t in and of itself dangerous, nor does it contain bacteria. It can, however, create secondary problems, especially in a finished basement.

“If it leaks and soaks into your carpet or gets into the drywall, over time it can produce mold,” Siv says.

If left unresolved, mold and mildew can grow quickly in a basement environment and lower the home’s indoor air quality.

Can a Dirty Filter Cause a Furnace to Leak Water?

Yes. However, this only happens when the furnace is used for cooling, not heating.

A dirty filter can block or limit the amount of air circulating through the system. The air conditioning condenser relies on this air to prevent it from getting too cold and freezing. If this air flow is limited, the condenser freezes up like a block of ice.

“When the condenser thaws, that water will end up on your floor in a puddle,” Smith says.

How Do You Fix a Furnace Leaking Water?

Here’s what a homeowner can do after finding a leaking furnace:

Should You Call a Pro To Fix a Furnace Leaking Water?

Yes.

If the pump drain tube is not the problem, you need to call an HVAC specialist to diagnose and repair the issue.

About the Experts

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