Dor-Mar Heating & Air Conditioner Service | Call Today, Service Today Guaranteed


Call Ohio HVAC Service Technician

Why is My Furnace Leaking Water? Explanation by an Ohio HVAC Technician

Is your furnace leaking or pooling water at its base? It’s not time to panic… yet. We’ll walk you through the troubleshooting steps first, then if you can’t resolve the issue yourself, one of our central Ohio heating technicians can help.

First, we need to determine if the furnace installed in your home is a “conventional” or “high-efficiency condensing” furnace.

Here’s a quick test to determine which type of furnace you have.

  • High-efficiency condensing furnaces use white PVC vent pipe that may go out a side wall or through the roof
  • Conventional furnaces use aluminum or galvanized steel venting, always vented straight up and out through the roof

It’s that simple!

Now that you know which type of furnace you have, you can jump to the appropriate section below for the correct troubleshooting tips.

  • Why Your High-Efficiency Condensing Furnace is Leaking Water
  • Why Your Conventional Furnace is Leaking Water

If you’re not confident in your HVAC troubleshooting skills, save yourself time and contact Dor-Mar Heating and Air Conditioning and we’ll dispatch one of our certified and highly trained service technicians to check out the problem.

Why Your High-Efficiency Condensing Furnace is Leaking Water

High-efficiency furnaces are actually designed to create condensation during the course of operations. Fortunately, that means the leaking can be resolved with a relatively minor repair.

We’ve found these three most common reasons that a high-efficiency furnace might be leaking:

  • Problems with the condensation line
  • Condensate pump issues
  • Condensate drain is blocked

Let’s examine why high-efficiency furnaces create moisture, and then we’ll describe how to resolve these three issues.

Why Do High-Efficiency Furnaces Produce Moisture?

High-efficiency furnaces contain two heat exchangers, the part of the furnace that transfer heat from the burner area through a sealed wall into the section of the furnace that forces the warm air out into the home. The two heat exchangers absorb heat so rapidly that the heated air gets converted to a liquid. Condensation forms, then is removed from the system through a condensate line.

If your furnace hasn’t been serviced properly so the condensate drain can remove the water, any leak or clog may cause an excess of water. That water usually appears pooled on the floor under your furnace.

How to Resolve a Condensate Leak

The first step to fix a condensate leak from your high-efficiency furnace is to check the drain trap. The drain trap can accumulate and trap dirt and debris, preventing the drain from properly performing its job. The easiest method to clear a clogged drain trap is to vacuum with a shop vac.

Other potential sources of condensate leaks are a broken drain line, a leaking condensate pump, or a leaking humidifier. If this is the issue, you’ll definitely want to book an appointment with one of our highly skilled HVAC techs. You can use the convenient appointment form located on this page, or simply call our closest location (see the list below).

Why Your Conventional Furnace is Leaking Water

When a conventional furnace is leaking water, again there are three common causes.

  • Improperly designed or installed vent pipe
  • Air conditioning is creating excess moisture, creating the leak
  • Leaking whole-house humidifier

Humidifier is Leaking

Check to see if your furnace has a whole-house humidifier installed. Water pooled around the base of the furnace could be coming from a clog or leak inside the humidifier.

Humidifiers need water to create humidity (moisture), so water is constantly flowing into, and out of, the system. Just like plumbing, over time any water-containing system can spring a leak.

Unfortunately, there’s not much you can do as a homeowner, if you identify a leak coming from the humidifier. Repairing this issue requires the skills of a trained HVAC service technician.

Improperly Designed or Installed Vent Pipe

A conventional furnace must have a metal flue pipe (vent pipe) installed, according to building codes.

The flue pipe is installed to safely remove combustion gases produced during the burning of fossil fuel inside your furnace. In a properly installed vent pipe, those gases escape outdoors (literally up the flue) before they can cool down, condense, and turn into water.

If the exhaust vent pipe is too large, or doesn’t have the proper slope, that could allow an excess of air to circulate, trapping gasses in the flue. The stagnant gas then cools in the fool, eventually forming into moisture and leaking out of the furnace into the area surrounding it.

Follow these steps to check the vent pipe:

  1. Inspect the flue pipe. Is there water dripping from it? Do you notice rust at the lowest point on the pipe? Is there no upward slope to the pipe?
  2. Call a Professional. This is a potentially complicated issue that needs a professional HVAC technician to resolve. He’ll ensure your vent pipe is the proper diameter and has the correct angle to eliminate any creation and collection of moisture. While he’s re-working the vent pipe, he’ll also seal everything to eliminate the issue moving forward.

Air Conditioning is Creating the Leak

If it seems your furnace only leaks while the AC is running, the actual problem is NOT the furnace, but the air conditioner.

One function of the AC, in addition to cooling the air, is to dehumidify it… meaning it absorbs moisture from the warm air in the home while it’s running.

Moisture usually drains from the HVAC system via a condensate drain. Just like with the high-efficiency furnace mentioned earlier, if that drain line is clogged or has sprung a leak, then water can find its way outside its normal path.

The condensate drain line is usually installed on top or, or next to, the furnace, making it appear the leak is coming from the furnace.

Here are steps to resolve a leak coming from the AC system:

  1. Confirm that you are running your AC and NOT the furnace.
  2. While the AC is running, shine a flashlight around the condensate drain line to look for the source of the moisture.
  3. If you determine the moisture is being created by the AC running, contact a qualified HVAC service technician to resolve the issue.

Still Not Sure Where the Leak’s Coming From?

If you’ve come this far and you’re still not sure where the moisture is coming from around your furnace, you should contact Dor-Mar to schedule a visit from one of our highly-trained HVAC technicians.

If you live in the central Ohio area, we cover communities from Dublin and Hilliard in the Columbus area, east to Zanesville and points beyond. We offer same day appointments if you have a no heat or no cooling situation.

Dor-Mar to the Rescue!

Schedule an appointment for HVAC system installation, troubleshooting or maintenance with us today by using our online contact form, or call one of our seven neighborhood offices listed below. We pride ourselves on our customer-focused service, and our reviews show it.

NEWARK  740.345.6639 • COLUMBUS 614.238.6689 • DUBLIN 614.545.8939 • REYNOLDSBURG 614.365.1579 • WESTERVILLE 614.381.1540 • GROVE CITY 614.595.3098 • ZANESVILLE 740.454.2420

Dor-Mar…Your Climate Hero!

*Please note: neither the Centers for Disease Control(CDC), the World Health Organization (WHO), nor the manufacturer of our UV-C Devices have officially announced whether UV-C kills the current strain of Corona Virus (COVID-19). We urge you to err on the side of caution until we have a definitive answer, and take other measures to prevent the acquisition or spread of this virus.


HVAC customer service in Newark, Ohio | Dor-Mar Heating & Air Conditioning

PLEASE NOTE: If you are a renter, please have your landlord/owner contact us directly to schedule service. We can only work with property owners.


Need a quick answer to a question? Enter your question below and we’ll get back to you with an answer. FAST!


Our Comittment to Your Family’s Health & Safety

Learn what we’re doing to keep you and your family, as well as our employees, safe from the spread of the virus as we service your heating and cooling needs.