Why Is My Furnace Leaking Water?

Posted on January 27th, 2021 by carrolladmin

Prevent your furnace from leaking water with regular maintenance, like this furnace in an older basement that needs to be repaired before winter.

When peak heating season is right around the corner, homeowners should have their HVAC systems checked. A tune-up after a couple seasons of downtime ensures your equipment works efficiently to provide quality comfort this winter.  

There’s a reason we emphasize seasonal maintenance

Seasonal maintenance is a comprehensive inspection of all HVAC system components.  We call it “seasonal” maintenance because it’s conducted during a specific window of time prior to peak usage months. 

Although furnaces are used during warm weather, check them for undetected problems prior to turning on the heat for the winter. This can help prevent water damage, inconvenience, and expense.

One of the most common problems is a furnace that is leaking water. There are several potential reasons behind this problem. We’ll discuss those in a moment. First, let’s explain the difference between a high efficiency or standard efficiency furnace. 

To determine which kind of furnace you have, check out the vent pipe. If it’s a white PVC pipe, it’s a high-efficiency unit. Standard efficiency units have metal exhaust pipes.  


Now that that’s out of the way, let’s take a look at the common causes of furnace leaks.

Common reasons for furnace leaks


High-efficiency furnaces create condensation. Some amount of condensation with these units is normal. When things are running smoothly, it goes through a condensation drain. 

An actual leak is typically caused by either broken or malfunctioning tubing, or a clogged floor drain. 

Standard efficiency units do not produce condensation, so any water is likely an indication of incorrectly sized flue pipes. When the pipes aren’t the right size, the hot exhaust from the furnace cools and condensates. The moisture then flows back through the tube pipe, causing a leak.

Both situations require prompt action.

Humidifier leaks: 

Many furnaces and HVAC systems come equipped with a humidifier. These units can leak for a number of reasons, like overly high water pressure and drain line clogs. While unlikely to happen with a well-maintained unit, if you’ve neglected preventative maintenance, call a professional right away.

Make sure that your drain line slopes downward–this is crucial to keep things running smoothly. Otherwise, air bubbles can form, backing the water up into the humidifier and causing leaking.

Additionally, pay attention to your water pressure. It shouldn’t be any higher than 125 psi.

Drain system clogs: 

When you have central air, an internal drain system operates both the air conditioning and the furnace. If air conditioning is still running, and both systems share a line, it could be routing water to the furnace. Systems with a combined drain line can also become clogged, resulting in a furnace that’s leaking water.  

A clogged drain system can cause leaks around the furnace. You may also spot tell-tale water leaks leading to the evaporator coils if you remove the access panel.

To prevent damage to floors, ceilings, and more, be sure to regularly replace your HVAC filters. You can also pour one cup of bleach into the drain line’s access hole, found near the unit.

What should someone do if they notice a leak? 

If you notice a leak, here are some steps you can take.

  • Turn off the unit. Shut down your heating/cooling system.
  • Don’t wait to clean up surrounding water. This helps prevent water damage.
  • Look at the filter. Check that the leak hasn’t affected airflow.
  • Remove debris/clogs. Use a water-safe vacuum on your PVC drain line.
  • Check the condensate pump. Pour water into the top. If it pumps the water, there’s likely no mechanical failure, and the drain line is clear.

Oftentimes when you have a heating or cooling emergency, drain lines and water backup is the cause. 

Any leaking or pooling water is an indication of a problem that you require immediate furnace repairs. Carroll Plumbing & Heating Inc.’s expertise includes all types of HVAC systems, as well as plumbing systems

Whether your issue is heating, cooling or plumbing related, our skilled technicians can quickly identify the issue. They’ll provide honest and reliable repair recommendations to get your system up and running again.

For help determining if your leak is a minor repair or major problem, contact Carroll Plumbing & Heating Inc. today or give us a call.

Learn How To Maintain Your Furnace