Furnace Leaking Water When Heat or AC is On: Causes and Troubleshooting

Leaking water soaking through the walls and floors of your house is never a happy sight. Water damage can cause a wide variety of problems for homeowners. It can seep into different structures through small openings, and cause extensive damage to wood framing, insulation, and drywall. It can also corrode metal frames and plumbing systems. This is not only detrimental to a house, but it can also indicate a faulty household appliance that may cause more damage of its own if it's not immediately looked after.

Leakages are especially common with heating and cooling units, and they usually lead to more problems as consistent moisture can breed things like mold and mildew. Mold and mildew are two forms of fungi that can grow in damp environments. They can cause health problems if they begin grow on your skin or in your lungs. Mold and mildew can produce allergens that can make you sick. Especially if you have asthma, it’s important to avoid exposure to mold and mildew.

Moisture in itself paired with any electrical equipment, is not a good sign either, as it can damage the parts. Water can ruin electrical appliances. Damage to the internal parts of an appliance can cause it to short out and stop working altogether. This is especially a problem with electronics, as water can cause corrosion and other problems that can make them fail. In some cases, even just a small amount of water can damage an appliance so badly that it needs to be replaced.

So all in all, we're trying to say that your furnace leaking water is something to be wary of. A quick clean-up with a mop isn't enough to prevent it from happening again. With enough furnace leaks, you might even start noticing a pattern. That is, your furnace might start leaking when you turn on your Air Conditioner or your furnace. In that case, there are specific ways to determine what's triggering the leaks.

At the end of the day, the best way to deal with leakage is to consult a professional so you don't risk putting yourself in harm's way. But if you just want to do surface-level research, these pointers below should help.

Causes and Fixes for When a Furnace is Leaking Water When the AC is On

Furnaces leaking when ACs are turned on is a common scenario across households, so these problems are generally easier to diagnose than leakages caused by heat.

A Frozen Evaporator Coil - A Furnace is Leaking Water When the AC is On

One of the most common reasons that lead to an air system leak is if the ACs Evaporator Coils are frozen because of reduced airflow. In such a situation, you're likely to witness water leaking all over the place once the AC finishes working, as this causes the ice to melt and leak in the form of water all over your floor.

Evaporator coils in air conditioning units work by using the heat of the refrigerant to evaporate water from the coils. This heat is then turned into cold vapor which is released and circulated around the unit. The evaporators rely on a steady airflow coming into the unit.

Usually, reduced airflow happens because of a clogged-up filter or a damaged drain pan that's allowing the moisture to freeze on the evaporator coils. Proper unit maintenance by regularly cleaning out the dust and debris blocking your air filter would help prevent this problem and dodge a bullet entirely.

A Blocked Condensate Pump - A Furnace is Leaking Water When the AC is On

If your AC is one of those models with a condensate pump to help the condensate from your AC coil to be exhausted outside, there's a possibility that you might run into a blockage or a clogging up. This, in turn, might lead to the condensate dripping out of your unit in a leak. In such cases, it's recommended that you check the drain pan or the drain hose to ensure it is not damaged.

If the drain pan doesn't show any signs of being the cause of this problem, then you can be sure that your pump has a part to play in this leakage. The easiest solution to this mess would be to repair or replace your condensate pump.

With so many tutorials online, any person with little mechanical experience should be able to repair the pump themselves, especially if they're dealing with a simple blockage. But, in general, most owners prepare to replace the pump entirely.

Either way, you must deal with your clogged-up condensate pump quickly because it can burn out the motor and decrease its lifespan considerably.

The Dehumidifier Problem - A Furnace is Leaking Water When the AC is On

If your AC has a dehumidifier or humidifier function (and most do) you might want to check their drain pans. Much like evaporator coils, the dehumidifier unit extracts moisture from the air and condenses it at low temperatures.

This moisture, then, is to successfully trickle down into the drain pan and be shed outside. However, a damaged drain pan could prevent this process from going smoothly and cause the moisture to leak out instead. With a humidifier, the water pipe could start dripping water.

For a leaking dehumidifier, the reduced airflow could be the main instigator again. Check the filters and the vents for blockages, and clean out any clogged-up spaces.

You might want to consider changing the drain pan if your air filter is not the problem. For a humidifier, check the water pipe's connection to the water supply, and make sure it's not cut or damaged anywhere.

Condensate Drain Pan - A Furnace is Leaking Water When the AC is On

As we've identified in the problems above, the drain itself could be the problem if it is damaged or dirty, as it refuses to collect the moisture from the other components and dispel it all out. Mold, dust, or debris left too long u cleaned on a drain pan can cause this.

You could also face a clogging up of the drain line that carries the moisture outside. In that case, you can clean it out by releasing water into it through a hose or compressed air in a can. If you don't want to deal with this problem personally, you can always call in a technician to fix this problem efficiently.

Causes and Fixes for When a Furnace is Leaking Water When the Heat is On

If you type out a Google search for help with a leaking furnace, you will likely come across many people reporting that their furnace leaks when their AC turns on. Fewer people deal with Furnace leakages when the heat is on. And for the few unlucky ones running into this problem, we've listed out some of the reasons why:

The Condensate Pump - A Furnace is Leaking Water When the Heat is On

A condensate pump in a furnace is used to move liquid or gas from one point in the furnace to another. This allows the furnace to work more efficiently by circulating heat around the metal parts.

Condensate pumps in furnaces that tend to carry the condensate upwards, rather than draining it downwards, can pose a problem, as you'll have to deal with possible blockages. Again, you can call in a technician to repair or replace this part or try to do some of your own repairings.

The Humidifier - A Furnace is Leaking Water When the Heat is On

Humidifiers in furnaces help to keep the air humidity at a certain level, which is important for comfort. When the humidity levels are too low, it can cause issues such as dry skin and respiratory problems. Furnace humidifiers also help to prevent fires from happening due to low oxygen levels.

Most ACs don't come with a humidifier, but usually furnaces do. The humidifiers are most likely to leak because they carry water to the unit. You might find a problem in the water pipe that fills the humidifier with water.

This might be because of an improper fitting of the pipe to the water supply or due to any cuts or damages on the pipe that are allowing the water to escape the pipeline, or you may be dealing with a blocked drain preventing the water from flowing out properly.

Some humidifiers even have pads that are supposed to absorb excessive water. However, minerals from the wage might make it hard and reduce its ability to soak up the water and prevent leakage.

The Condensate Drain - A Furnace is Leaking Water When the Heat is On

If you have a condensate furnace as opposed to a non-condensing one, then you will be dealing with moisture and leakages a lot more than a non-condensing furnace owner. This type of furnace is used to heat water, steam, or other gases so that they can be turned into liquid form. In a house, this may be used to heat water or air.

A condensate furnace exhausts a mixture of gas and propane as it works, and gas is made up of water vapor. If your furnace's vent isn't working properly, and the moisture isn't being drained out as it should, there are increased chances of leakage.

The Heat Exchanger - A Furnace is Leaking Water When the Heat is On

Cracked heat exchange is a common cause of the problem of a leaking furnace. The Heat Exchanger transfers heat from the combustion chamber and sends it out to the rooms through the vents.

This combustion exhaust contains moisture, which should typically be drained out through a vent or condensate drain outside the house. However, this might be disrupted if your heat exchanger is damaged, as it stops the proper disposal of moisture from the unit. Instead, the moisture might leak out right back into your home.

If you have a Carbon Monoxide detector to alert you, then you know where the problem lies.

While most components behind a water leak are small and repairable, a heat exchanger is more serious. Especially because a damaged heat exchanger indicates the end of a furnace's life, you're better off simply replacing your whole furnace instead of spending unnecessary money trying to repair the part.

A cracked heat exchanger isn't something that occasionally happens because heat exchangers only show signs of wear and tear after they've exhausted their usability.

You shouldn't be putting up with a water leakage for different reasons. A water leak is neither safe nor hygienic for you, nor is it a good sign about the condition of your AC or furnace. This is why you must take the appropriate measures to deal with it effectively.

Conclusion - Furnace Leaking Water When Heat or AC is On: Causes and Troubleshooting

It's never a pleasant sight to see water seeping through your house's walls and floors. It is crucial to take care of leakage problems in your air system right away because water damage can result in a wide range of concerns for homeowners.

Individuals can definitely repair their own furnaces and AC units. You might even learn after diagnosis that your air system only requires a quick cleaning. You should be able to repair your own furnace or air conditioner as long as you have the right tools and follow the right safety procedures.

However, you might think about hiring someone else to fix your air system if you don't feel confident doing it. It may occasionally be safer and more effective for a qualified professional to examine your heating system, especially for complex problems.