Furnace Exhaust Pipe Leaking Water: 5 Causes & Fixes

Spotting water where it does not belong can be a real headache especially if you spot a puddle of it under the furnace which does not need any water to operate.

Your first thought on seeing water leaking from the furnace exhaust pipe might be that something is wrong with the furnace and to be fair the reality is probably not so different as water leakage from the said area is indicative of some complex problem inside the furnace or the HVAC system.

A water-leaking furnace exhaust pipe needs immediate attention because it also means that the pipe is emitting carbon monoxide and carbon dioxide, both of which if leaked back into your house can prove to be dangerous.

5 Causes of Furnace Exhaust Pipe Leaking Water and How to Fix It

Furnace Exhaust Pipe Leaking Water

Conventional furnaces have nothing to do with water and should not be producing water at any point whatsoever. A furnace exhaust pipe leaking water is a definite anomaly and needs to be remedied, both for the safety of the people inside the house as well as for the HVAC system itself.

However, if your high-efficiency furnace is leaking water then it may be from other appliances such as the AC.

The question is, why does this happen? Well, there can be a handful of reasons for both types of furnaces and they have been outlined for you along with some easy ( or not so easy) fixes!

Leaking Humidifiers

The one thing HVAC systems and furnace is infamous for is removing humidity from the air which can get quite uncomfortable for people who have to constantly breathe in dry air. This is why some people add a humidifier to the furnace so that it can combat the dry effect a gas-powered furnace has on the air.

Now, all humidifiers need water as a source for the moisture and humidity it adds to the air and this source may become a problem if the connection between the humidifier and the furnace develops a leak or if the humidifier itself is damaged and cracked.

The connectors between the furnace and the humidifier are most prone to such leaks. To be specific, the water supply line, the automatic valve that allows the water inside the humidifier, the feed line, and lastly the casing that houses the humidifier.

Any crack in these areas will leak water in the vent pipe and subsequent leakage of water in the furnace exhaust pipe.

Solution: If the leak is on the supply line, then you can use duct tape and plumbers tape to securely tie it around the leak.

You can apply the same method if the crack is on the humidifier casing but for the other inaccessible parts, you should call a technician so as to not disconnect or destabilize any of the existing joints that connect the furnace and the humidifier. 

Fault in the Vent Pipe

The vent pipe in a non-condensing furnace is responsible for transporting the combustion gasses such as carbon dioxide and carbon monoxide outside the house.

Sometimes the design of the pipe is not compatible with the furnace or maybe there is some problem in the installation that stops the pipe from performing properly.

In such a case water may condense back from the gasses in the vent pipe and leak back into the house and cause water dripping from the furnace exhaust pipe.

Solution: If you suspect that the vent pipe is the culprit behind the presence of water in the furnace exhaust vent, then immediately call an HVAC technician.

It means that the water is being condensed out of the combustion gasses that were supposed to go outside your house but now will be inhaled by you instead. These gases included carbon monoxide from the furnace and there’s no need to reinstate how lethal the gas can be.

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The condensate Pump is Leaking

The condensate pump in a high-efficiency furnace is where the condensate drains into. This is a component that can get clogged due to debris and cause a blocked drain which will lead to the furnace exhaust pipe leaking water.

If you spot water spilling on the floor under your high-efficiency furnace or rust within the cabinet then, it means that your furnace has a blocked drain channel and is not able to dump the condensate properly which is why it is leaking back through the exhaust pipe.

Solution: Unfortunately, it is quite usual for condensate pumps to break down and stop functioning after four to five years of damage, so the pump you have may need to be replaced as repair will just be a waste of money and time at this point.

In any case, it will best to consult with a trustworthy HVAC technician regarding this issue.

Clogs in the Drain Channel

A furnace collects air and air usually has a lot of debris and dust particles which are allowed to accumulate for a long time and can form a substantially surprising amount of debris, just enough to block any part of the drain system. This means that the moisture that was to be guided outside of your home will now be leaked inside instead.

Solution: If the clog has formed where the drain line connects then if it’s in an accessible place then you may be able to remove the access panel from the drain pan/collection pan and unclog the blockage.

Be sure to not push the debris further into the blockage because it will be harder to remove then. You can always call a plumber to do this for you as removing the drain lines have to be done carefully.

Water leakage from the AC in a non-high-efficiency Furnace

In a standard efficiency furnace or a conventional furnace, there is no question of water generation from anywhere so if you notice water in the furnace exhaust of the furnace then it is probably from associated appliances such as the AC.

Now the AC most definitely generates water and there are multiple reasons why it will leak through the furnace exhaust vent. It can be a rusted or broken drain pan, a frozen evaporator coil, dirty air filters, a blocked drain channel, or just a damaged condensate pump.

Many of these reasons are even interconnected as dirty air filters may cause the evaporator coils to freeze and this ice may be manifested both from the AC vent as well as the furnace vent in the form of water.

Solution: If the culprit is a dirty air filter and a frozen evaporator coil then it can be fixed at home. All you have to do is remove the access panel and clean the filters. For the evaporator coils, you can hold your blow dryer near the vent and melt all the ice.

As for the other issues, you are going to need a professional for dealing with those.

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Wrapping Up

Although already mentioned, the water near the furnace is a cause for concern.

In any case, you should call for repairs at the earliest as it concerns both the safety of the people living inside the house as well as the furnace itself which may need costly repairs if the problem is allowed to persist.

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