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Pacific Sheet Metal Blog

Why is My Furnace Leaking Water?

Posted by Joey Haack on Aug 9, 2022 10:45:00 AM | Updated on 08/09/22 12:45 PM



Water damage can be detrimental to a house, and unfortunately, many homeowners like yourself have experience with this. Water leaks, like those from a furnace, can be a major headache and lead to high repair costs, mold growth, and if left unchecked, a complete furnace replacement.


You should never be able to see water around your furnace, even though you may hear it. Here are a few common causes of a furnace leak, how to prevent them, and what to do as soon as you notice this issue in your own home.


Causes of a Furnace Leak


Condensation/Drain Pan


As your air conditioner runs, the pan underneath the coils fills up with water. If this pan becomes too full, some water may drip out of the furnace. A simple fix for this type of issue is to empty out the pan, clean it, and put it back. If the leak continues, you’ll need to check other aspects of the unit for the source.




If you own a high-efficiency furnace, the leak may be due to condensation. High-efficiency furnaces extract heat from combustion gases for a long period of time. The gases cool down, then condense. That condensation is routed through tubing to a floor drain. So, when either that tubing or floor drain get clogged or damaged, a condensation leak can occur.


Keep in mind that only high-efficiency furnaces produce condensation. If you see water pooling on the ground but have a standard-efficiency furnace, the culprit could be another appliance close by.


Humidifier Damage


The furnace’s humidifier can also be the source of the leak. In order to add moisture to the air, the humidifier needs plumbing to obtain water. If the water lines crack or get clogged, it can result in a water leak. While this type of leak may not seem very urgent, it can cause an incredible amount of water damage if left alone. A leaking whole-house humidifier can cause extensive damage to the inside of your furnace, and the issue can spread to your walls and floors.


Clogged Furnace Filter


Your furnace uses a filter to clean the air in your home. When these filters aren’t changed on a regular basis, they can become very dirty and clogged, which restricts airflow through the furnace coils. A clogged filter can cause those coils to freeze, resulting in water leaking from the unit.



Preventing a Furnace Leak


Regular maintenance on your air conditioner and furnace will do wonders in preventing future leaks. Once every three months (or sooner if necessary), replace the air filter. If you have the skill and confidence, you can make sure all burners and the flame sensor are cleaned, as well as the humidifier. Ensure there are no loose electrical connections, then inspect the heat exchanger for damage. The fans within the furnace need to rotate freely and may need to be lubricated. Lastly, clean any registers and ductwork to maximize airflow.


For those of us without the necessary skill to perform this maintenance on our own, it is important to schedule this yearly with your local professional technician.


How to Fix a Furnace Leak


Once you notice your furnace is leaking water, it’s important to act as quicky as possible to isolate the damage. Waiting too long can lead to expensive repairs and major water damage throughout your home. First, shut off the furnace and clean up all the water around the unit. Check the filter to ensure airflow isn’t impacted, then dump out the condensation/drain pan and replace it.


Unless you have extensive knowledge of the innerworkings of your furnace, your next step is to contact a professional. They will be able to diagnose the problem in an efficient and timely manner.


A furnace leak can be concerning, but acting quickly once you notice the problem can be the difference between minor and major water damage. Subscribe to our blog for more advice on keeping your home safe.

Topics: heating and cooling