A furnace leaking water in winter? Many people aren’t even aware that certain gas furnaces — specifically, high-efficiency models with efficiency ratings of 90 or above — actually generate substantial water during normal operation. High-efficiency furnaces incorporate a secondary heat exchanger to extract additional heat from exhaust gases, a process that also condenses water from the gases. A high-efficiency home furnace may produce five or six gallons of condensate per day, depending on its hours of operation.
Where Does All the Water Go?
Here’s how water moves from the furnace to the outdoors:
- The flow of condensate passes from the secondary heat exchanger and through a trap that prevents dangerous combustion gases from leaking into the house, and then goes into a plastic collector.
- Condensate then flows into a PVC drain pipe that extends through an exterior wall to the outdoors. There, the water drips into the ground and is absorbed.
- Condensate may flow freely due to simple gravity flow. However, depending on the routing of the PVC drain pipe, an electric pump may be needed to push the liquid through the pipe to the outdoors.
How Does Leakage Happen?
A furnace leaking water in winter can be the result of several issues:
- A clog in the trap or the drain pipe. This will cause condensate flow to back up and eventually leak out inside the furnace, ultimately forming puddles on the floor.
- Leakage at the condensate pump (if present) or in the PVC drain pipe. Most condensate drain pipes include fittings to join segments, and leakage may occur at one of those fittings.
- Ice forming at the outdoor end of the pipe during freezing weather, causing a condensate backup and overflow.
What Should I Do About a Furnace Leaking Water in Winter?
Because of the complexity of the drainage system and critical safety factors relating to the condensate trap, tracing and resolving condensate leakage in a high-efficiency furnace is a job for a qualified HVAC professional. If you notice signs of water leakage, shut down the furnace, mop up the puddles, and call for professional help.