Why Is My Furnace Leaking Water?

Furnace repair

If you believe your furnace is leaking water, it is essential to determine if it is definitely leaking right away. Addressing the leak early, before it becomes an issue, can help you avoid higher repair costs, bio growth, and health risks.

Your furnace can leak at any time of the year for multiple reasons. Whether it is due to water condensation or a frozen coil, it is necessary to identify the leak as soon as you can.

What Does a Furnace Leak Look Like?

When water is leaking from your furnace, you will notice a puddle of water on the ground near your furnace. It is definitely leaking if you see that the puddle of water gradually increases in size.

Detecting a furnace leak as soon as possible is crucial, as a leaking water problem is a considerable concern for a homeowner. In addition to a puddle of water nearby, you might notice cracks on your furnace or strange smells.

Why Is My Furnace Leaking Water In the Winter?

A few common reasons are that your furnace can leak water in the winter.

Flue Pipe

If a flue pipe is not fitted correctly, there might be condensation due to the heat produced from the heat exchanger. If the flue pipe is not installed correctly, the pipe can leak water and it can end up on your floor.

Condensate Pump

A problem with the condensate pump happens only with condensing furnaces. These furnaces have a condensate pump to help push the condensation created within the furnace out to the pipe. If the condensate pump isn’t functioning correctly, it can cause water to back up and leak.

Secondary Heat Exchanger

A secondary heat exchanger soaks up combustion exhaust from the primary heat exchanger, releasing the excess heat. This may cause water vapor to form. If your secondary heat exchanger malfunctions, it is often a warning that your furnace is coming to the end of its life.

It is often suggested, at this point, to replace your furnace instead of repairing it, as this is the most cost-efficient. Some signs that your secondary heat exchanger is broken include cracks in the fan compartment, water dripping along the cracks, or signs of corrosion.

Why Is My Furnace Leaking Water In the Summer?

These are the most common reasons your furnace leaks in the summer.

Clogged Filter

If the filter is clogged, airflow is reduced through the coil. This might cause your coil to freeze, causing water to develop. You can identify your clogged filter if your energy bills or air pollution within your home has gone up. A clogged filter can be avoided by changing your furnace filters before becoming clogged.

Drain Pan Has a Leak

Sometimes your furnace may leak if your drain pan below the coil leaks. If the water has rested too long on the coil, holes, and rust can develop, allowing water to drain through it. If your drain pan leaks, you will notice a pool of water around the furnace, cracked or holes in your drain pan, debris, or clogging.

Defective Blower

If you notice icing or frosting on the evaporator coil, you may have a defective blower. It is normal for defective blowers to fail over time, especially if you have had your furnace for 10 to 20 years. If you have tried to clean the blower, start your furnace, and still have no luck, it is likely broken, and you need to call a professional.

What Do I Do If My Furnace Is Leaking Water?

If you believe your furnace is leaking, turn off the switch on your unit and the breaker. Clean up the water that has settled on the floor by your furnace.

If you have checked the air filter, blower, drain pan, flue pipe, condensate pump, and secondary heat exchanger and are unsure why your furnace is leaking water, it might be best to call a professional HVAC specialist to help.

Why Is My Furnace Leaking Water? FAQs

Why is there water leaking from the bottom of my furnace?

Water may leak from your furnace due to a clogged filter, defective blower, drain pan, flue pipe issue, condensate pump, or secondary heat exchanger. However, it could be a different issue that is less common. An HVAC professional can help determine and resolve the issue.

Is a furnace leaking water an emergency?

A furnace leaking water can be an emergency, especially if it leaks a lot. It can cause severe water damage or health risks due to bio growth if the leak is not resolved.

Can a dirty filter cause a furnace to leak water?

Yes, a dirty air filter can become clogged, causing your furnace to leak water. You should replace your filter once every three to six months to prevent it from becoming clogged.


There are multiple reasons that your furnace may be leaking, and any of these reasons can happen at any time of the year. If you believe your furnace is leaking, call a professional HVAC repair service to help determine the cause, repair the leak, or possibly replace the furnace altogether.

Southwest Heating and Cooling can help find the cause of your leak. Let us handle your furnace needs!

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Contact the experts at Southwest Heating & Cooling.

Call us at (303) 791-2679!