While many newly-built homes in the U.S. have electric heating over gas or biofuel heating, there are still many homes that use gas heating. Furnaces are typically the most common heating system in homes. While many modern furnaces are fairly reliable, it’s still very important to regularly check on the health of your furnace. A leaking furnace can become pretty dangerous when left unchecked.

Seeing a dreaded puddle on the floor near your furnace can be nerve-wracking. However, learning the causes of a furnace leak will make it easier to prevent them in the future. 

Before we can answer the question of “Why is my furnace leaking?”, let’s take a look at the different types of furnaces.

How Does a Furnace Work?

There are two types of furnaces: a standard-efficiency and a high-efficiency. The biggest difference between the two is that a high-efficiency furnace produces condensation, while the other does not. 

Both furnaces function the same up until the cool air from inside your home is blown into a heat exchanger. A high efficiency furnace has a secondary heat exchanger, while the other only has one. 

The air goes through a second heat exchanging process when it enters the other exchanger, and this is where the condensation is created. As the water vapor transforms into liquid, it releases more heat into the second heat exchanger. The condensation should then be drained into a condensate pump or a floor drain. 

Determining What Kind of Furnace You Have

The exhaust pipe is the best way to determine whether you have a standard or high- efficiency furnace.

A standard-efficiency furnace will have a metal exhaust pipe. Meanwhile, a high-efficiency furnace will have a white place PVC exhaust pipe.

Why Is My High-Efficiency Furnace Leaking?

Typically, a water leak in a high-efficiency furnace is caused when the condensation that the furnace produces cannot be drained correctly.

These are the parts of your high-efficiency furnace that can cause leaks if they are cracked, clogged, or damaged:

  • Condensate drain hose: The drain hose sloped down away from the exhaust pipe, so it can become clogged quite easily with dirt or other debris. 
  • Inducer assembly: The condensation produced by the furnace runs down the exhaust pipe, through the drain house, and then into the inducer assembly. When it is cracked, the condensation may leak out.
  • Condensate drain line: The exiting water passes through this drain line. Therefore, if has a loose connection, cracks, or holes the water will leak. A clogged drain line can also cause leaks since the condensate will be backed up.
  • Condensate trap: Not every high-efficiency furnace has one, but the issue here is similar to a clogged drain line; if it is clogged the backed-up condensate will overflow out.
  • Condensate pump: This is the condensate is drained to. The pump can also clog, which causes a leak. A malfunctioning pump can have the same issue as a clogged one. In this scenario, the pump would need to be replaced.

The best way to ensure that your furnace is running as smoothly as possible is to regularly examine the unit. You can do this yourself, but you should also hire a professional to regularly inspect your unit.

Why Is My Standard-Efficiency Furnace Leaking?

Since these conventional units do not produce any water, the leak is most likely caused by another appliance you have nearby. Your air conditioning unit, hot water heater, and humidifier are all appliances that produce water and have various parts that can break.

For example, your AC unit could have a frozen evaporator coil, or a damaged drain pan. Your water heater could be cracked or have a loose valve. Your humidifier could have cracked or clogged lines. 

Just like caring for your furnace, it’s important to regularly inspect all of your HVAC units.

The Dangers of Water Leaks

While furnace leaks are usually not huge, they can still pose a danger to you or your family. Water can cause rust and mold, which are both detrimental for different reasons. 

Rust can cause further damage to your furnace parts, which will mean that they will need more repairs in the future. Mold can cause sickness as well as damage to your home. The water can also damage other porous surfaces like drywall or insulation.

For these reasons, it’s crucial that you call a professional to assist you immediately if you notice a leaking furnace. It’s important that you also turn your HVAC system off and clean up the water while you wait for the professional to assist you.