All of you must be aware of the fact furnace is something that help us stay warm during the winter season but it is a troublesome experience when the furnace starts leaking. It is possible that people confuses a leaky furnace with a plumbing problem. However, some of the common causes of a leaky furnace are the following:One of the most common causes is when the furnace gives off condensation. This happens when the flue pipe is not sized properly. The result is that the exhaust cools and condenses in the pipe which in turn goes back to the pipe and it starts leaking.Another cause when there is a clogging in the internal drains. When the drains are clogged the water is redirected to the pipes which in turn cause water leakage.A leaky humidifier inside the furnace is also another cause that causes leakage of the furnace. However, in case you have a leaky humidifier you need to be careful because that could cause serious damage to the furnace.One of the most costly repairs of furnace leakage could be when the heat exchanger starts malfunctioning.