Why is my furnace leaking water?

Furnace water leaks are typically caused by condensation issues, a clogged drain, or problems with the heat exchanger. Most water leaks are related to normal condensation that isn't draining properly, but some causes require immediate professional attention.

High-efficiency furnaces (90%+ AFUE) produce condensation as part of their normal operation. This water should drain away through a condensate drain line and floor drain. If you see water pooling around your furnace, the most common culprit is a clogged condensate drain line or a blocked floor drain. The drain line can become clogged with algae, debris, or ice during winter months, causing water to back up and leak around the unit.

Mid-efficiency furnaces (80% AFUE) shouldn't produce condensation during normal operation. If you see water around an older furnace, this could indicate a cracked heat exchanger, which is a serious safety concern. A cracked heat exchanger can allow combustion gases (including carbon monoxide) to mix with your home's air supply, creating a dangerous situation that requires immediate professional attention.

In Ottawa's climate, frozen condensate lines are also common during extreme cold snaps. The drain line that exits your home can freeze, causing water to back up into your basement. Other potential causes include a faulty humidifier connected to your furnace, improper venting, or issues with the furnace's internal components.

Safety is paramount - if you smell gas, hear unusual sounds, or suspect a heat exchanger problem, turn off your furnace immediately and call for emergency service. For condensate drain issues, you can check if the floor drain is clear, but avoid attempting repairs on gas components yourself.

Next steps: Turn off your furnace and contact a licensed HVAC technician to diagnose the leak source. In Ottawa, this type of service call typically costs $150-250, and repairs can range from simple drain cleaning to more extensive component replacement depending on the cause.

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