There could be a few reasons why your furnace is leaking water, but let’s start with the most likely one: a condensation leak.
High-efficiency furnaces — those with an Annual Fuel Utilization Efficiency (AFUE) rating of 90 percent or higher — have cool exhaust, and as a result, they produce condensation. An easy way to tell if you have a high-efficiency furnace is to look at its vent pipe. If the pipe is white plastic (PVC), you have a high-efficiency furnace.
Typically, the condensation from a high-efficiency gas furnace is channeled to a floor drain. Your leak could be a result of the condensation tubing becoming clogged or from breaks in the line. It could also be a result of the floor drain becoming clogged.
A standard-efficiency furnace — which has a metal exhaust pipe — should not have condensation. If it does, it could mean that the flue pipe was incorrectly sized. That could allow the hot exhaust to cool down and condense in the pipe, then drain back to the furnace and leak out.
Faulty furnace secondary heat exchanger
If you don’t have a furnace condensation issue, it’s possible that the secondary heat exchanger is the source of water around your furnace.
Let’s hope not, though. That could be an expensive fix, and it might even require a complete furnace replacement.
Issue with furnace humidifier
You could also have an issue with your humidifier, which could be leaking inside your furnace.
If you’ve had an annual HVAC service check, as you should, this is an unlikely scenario because your service technician would have alerted you to the issue early.
If you have neglected that tune-up, you should call for it now because if this is your problem, the leak could do a lot of internal damage to your furnace.
Internal drain system clog
There is another possibility. If your air conditioning unit is still operating and it shares an internal drain with your furnace, you could have an internal drain system plug, which is sending water to the furnace.
While we can’t diagnose your issue precisely, don’t let this go too much longer. It’s a clear sign that you need to call in professional help.
Leaks can cause huge issues, including damaging parts, flooring and walls, and lead to mold growth. A reputable heating and cooling specialist should be able to quickly diagnose the source of the leak and offer solutions to your water furnace problem.