The Mr. Furnace Blog


If your furnace is leaking, chances are you’re quite concerned about it. A leaky furnace is not likely to run at its best, and the water can damage your floors and walls. It’s best to take care of a leak as soon as it starts. But what causes furnace leaks? There are several possibilities.

High-efficiency furnaces are equipped with a cool exhaust. Because of this, condensation is formed. You can tell if your furnace is high-efficiency by looking at your vent pipe; if it’s white plastic (PVC), your furnace is a high-efficiency model. Usually, the condensation in high-efficiency furnaces gets channeled into a floor drain. If you have a leak, it could be because the tubing for the condensation has become clogged or cracked. The drain in the floor might also be clogged.

If your furnace doesn’t have a white plastic vent pipe but has a metal exhaust pipe instead, then you have a standard-efficiency furnace, and there should not be any condensation. Condensation in a model like this indicates that the flue pipe wasn’t sized correctly, allowing the hot exhaust to cool and condense while in the pipe and drank back to the furnace and leak onto the floor.

If that weren’t the issue, then it could be your secondary heat exchanger. However, you wouldn’t this to be the case since it can be very expensive to fix and may even require you replacing your entire furnace. If you suspect that this is the problem, do not hesitate to contact a trained professional to take a look.

Another possible cause of water leakage is the humidifier. Sometimes they leak inside furnaces, allowing water to collect and potentially cause a lot of damage to your furnace. Regular tune-ups will catch problems like this, so if you haven’t had a furnace tune-up, you should schedule one right away and make them a regular part of your routine in the future.

An internal drain system clog could also be the culprit. If you have an air conditioning unit that shares an internal drain with your furnace, there might be an internal drain system plug that is forcing water into the furnace. This is a situation that requires immediate help from a trained professional. Do not put this off!

Water leaks can cost you a lot of money if they’re not dealt with right away. Mold damage, rotten wood floors, damaged wallpaper, ruined carpet, and much more can happen when an unchecked furnace leak runs its course without intervention. Be sure to have regular furnace checkups to watch for potential problems, and have Mr. Furnace’s number handy for emergencies when you need someone to come right away.

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