Household furnaces produce heat by burning fuel, usually natural gas, in a contained space and then transferring the heat via an intermediary medium. Specifically, a furnace that uses water as the intermediary is more commonly known as a boiler. There are other types of furnaces that use forced-air as the intermediary and, believe it or not, they also suffer from furnace leaking.

Aside from the obviously disconnected pipe that delivers water to the system, there are several other possibilities for that puddle of water underneath your furnace.

Many furnaces are part of a consolidated heating, ventilation and air conditioning, or HVAC system. All cooling, heating and humidifying are delivered via the same ductwork. As such, the air conditioner, heater and humidifier are all located near each other. Usually, the AC unit is installed above the furnace with the humidifier located below. Furnace leaking can originate from any of these components. Here are a few tips on isolating the problem of furnace leaking:

1. Start with the obvious and check the pipes again for any obvious signs of leaking. If found, disconnecting and properly replacing a poorly made connection should remedy this problem.
2. Next, examine the evaporator coil in the AC unit. There is just no preventing the condensation that will occur while this unit is functioning. Clean the drain pan and make sure that the drain is unclogged and that it is directed into the external drain in the floor.
3. Malfunctioning humidifiers are a prime cause of large leaks. If the humidistat, the device that measures and controls the humidity, is malfunctioning, excessive amounts of water will be delivered to the system. This excess water will condense on the AC coils and result in a leak below the furnace.
4. The heat of a high-efficiency furnace creates a remarkable amount of condensation and can cause pooling below the furnace if the drain is clogged. If the liquid has a noticeably oily feel, then this is your problem. This leak is particularly troubling as the condensate is highly corrosive and should be remedied immediately by cleaning and unclogging the drain pipe.

Each of these problems requires some time and energy to solve but a tenacity will pay off. As a first step, concentrate on narrowing down the possibilities as the actual problems are not that difficult to fix once you have isolated the problem of furnace leaking. If you’re still uncertain as to where the leak is coming or even if you have found the leak but unable to repair yourself it is best to call a heating contractor to remedy the furnace leaking before it starts to do damage to your heating system.