Is Your Furnace Pipe Dripping Water? Top Possible Reasons + Fixes

Kenneth Wilson

Do you see water dripping from your furnace PVC pipe? Don’t worry. There’s no need to panic– at least not yet. Homeowners usually notice this issue during their monthly HVAC system maintenance. So once you see water leaking from a furnace exhaust pipe, this may suggest further issues you need to sort out at once.

For instance, if the furnace exhaust pipe leaks water, it may also leak combustion gases (carbon monoxide and carbon dioxide). The last thing you’d want is to let these harmful gases find their way inside your home! Since there are several possible causes for water dripping from the furnace PVC exhaust pipe, let’s look at the most common reasons below.

6 Common Reasons for Water Dripping from the Furnace Pipe

We’ve listed below all the possible reasons there’s water dripping from the furnace vent pipe.

1. Condensate Pump Problems

Several condensing furnaces utilize a condensate pump to remove water from the furnace and bring it to the drain. Once the condensate pump fails to function as intended, the condensed water will eventually overflow the tank and start to puddle around your furnace. The solution? Opt to have the condensate pump repaired or replaced if the entire pump assembly is beyond saving. A trained HVAC technician can only do this.

2. Furnace Condensation

Homeowners with a high-efficiency furnace may deal with excessive condensation problems. If you’re unsure whether you have a high-efficiency furnace, check the vent pipe if there’s an attached PVC pipe.

Any leak may be due to a clogged condensation tubing or floor drain. In simple cases, you may be able to fix the problem using commercial tablets and installing a larger drain hose. But if you have a metal pipe attached to a standard-efficiency furnace, keep in mind that it must never leak condensation. If you notice water dripping from the furnace pipe, you may have the wrong exhaust pipe size for your unit.

3. Improperly Designed Vent Pipe

For non-condensing furnaces, the combustion gases are vented out of your home and through the roof using a metal flue pipe. If it was incorrectly installed, chances are the combustion gases won’t be able to escape your house correctly. Here are some of the most common associated problems with an improperly working vent pipe:

  • The failing vent pipe is unable to vent the hot gases outside properly
  • Your furnace may struggle to operate correctly due to the leak
  • The water may condense out of the combustion gases and find its way indoors
  • Combustion gases may leak inside your home

When you notice that your flue pipe isn’t operating correctly or if you suspect an improper installation, it’s best to consult a local HVAC technician to assess the problem. A leaking furnace vent pipe can put you at risk, as both carbon monoxide and carbon dioxide can be lethal.

4. Furnace Humidifier

If there’s a humidifier installed beside your furnace, it may be the culprit behind the puddle of water. Humidifiers add moisture to the warm air inside your home, effectively preventing dry air.

But, owning this unit means you are most likely to eventually stumble across humidifier-related problems such as a clogged drain or filter. Water might also leak from different points in the unit. It may leak at the connections, or the unit itself may corrode and leak after some wear and tear. Ask a professional to assess the condition of the humidifier unit, find the cause of the leak and fix the problem.

5. Clogs and Plugs

Clogs and plugs may develop in your drain system, considering how furnaces are prone to debris that may eventually turn into plugs. Sometimes, it may start in the drain pan and form where the drain line connects. You may be able to remove the access panel for the collection plan to remove the clog effectively, but this will depend on where the drain line connects. Avoid pushing the material down the drain line, as this will require more labor-extensive work on your end to clear the blockage.

We strongly recommend hiring a local plumber or HVAC professional to inspect your drain lines and the system to remove the clog successfully. You can count on their expertise to avoid dealing with more pressing issues.

6. Secondary Heat Exchanger

Your furnace’s heat exchanger draws the line between the combustion process and the breathing air circulated indoors. Once the air is blown across its hot metal surface, it will be warmed enough before being distributed throughout the home.

It is one essential component of your furnace. Due to metal fatigue, however, these heat exchangers will need timely replacement. Note that heated-up metal typically expands, and once it cools off, it tends to contract. Think of it as bending a thin piece of metal. Expansion and contraction will eventually break a heat exchanger.

Water passing through the breach may suggest a possible crack or hole in your heat exchanger. Avoid severe problems by having them assessed and replaced by a professional at your earliest convenience. The sooner you take care of this problem, the better!


Whether you have a standard furnace or a condensing unit, the moment you see water dripping from the furnace vent pipe is a matter of concern. It shouldn’t be taken lightly– as this can expose you and the rest of your family to harmful gases. Not to mention, overlooking this problem may lead to more expensive repairs or a total catastrophe at home.

It’s best to contact an HVAC technician in your area if you are dealing with the issue of water dripping from the furnace pipe. They can help you assess the situation, present you with the best course of action to take, and have the problem fixed.

Other Possible Problems

It may be a sign that you have a roof issue rather than a furnace problem if the water you observe runs down the vent pipe to your furnace while it is not working. The vent cap where the furnace vent pipe exits the roof may also leak.

Consult a roofing professional to examine your roof, the vent pipe cap, and the vent installation if you think your roof may be leaking. A roofing contractor can advise you on the best way to handle the problem. (Related: Why Is My Furnace Leaking Water? Let’s Figure It Out)

Frequently Asked Questions (FAQs)

Why is my furnace exhaust pipe leaking water?

The exhaust pipes of high-efficiency furnaces usually leak. Why? Condensation buildup in your high-efficiency furnace is, in fact, normal. Condensation typically drains via a pipe and exits your home safely through a floor drain. However, occasionally your pipe could get clogged, or there could be a split in the tubing, causing a condensation leak that damages your home. To stop the leak in the exhaust pipe, you must patch the leaking tubing.

Do you need professional help with furnace leaking water?

Most of the time, a professional assessment of your furnace is necessary. You don't want to make matters worse and pay for more costly repairs due to severe issues. The difficulty of disassembling and reassembling the furnace is usually the main reason you need a specialist. Contacting your local HVAC company to see if they can assist you with furnace water leaks is one of the best things you can do. (Related: Furnace Leaking Water? Common Causes + What to Do)

Why is my furnace exhaust pipe leaking gas?

A condensation leak in your furnace's exhaust pipe may indicate gas leaks. If neglected, this could develop into a significant problem. Look for bubbles in the place where the water is leaking from. Hire professionals to check your property and the pipe for carbon monoxide leaks.

Kenneth Wilson
July 19, 2022
Contractor Tips, HVAC

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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