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A nice puddle to jump in after a rain shower leaves you with a fun, happy feeling. Finding a puddle of water that has leaked from your furnace – not so much. A furnace leaking water doesn’t usually mean a huge repair bill, so don’t worry just yet!

You will need an HVAC service professional to inspect and test the unit in order to diagnose this with certainty, but here is some information to give you a little insight into if you may have this type of leak.

High Efficiency Furnaces are more likely to leak

These furnaces extract more heat from the combustion process by cooling the exhaust gases below their dew point. This creates condensation, which is typically acidic. To handle this condensation, high-efficiency furnaces are equipped with a secondary heat exchanger that allows the system to capture more heat from the combustion process. The resulting condensate needs to be drained away.

Traditional furnaces, on the other hand, release the combustion gases directly into the flue without extracting as much heat. As a result, there is little to no condensation generated within the system.

If you do have a furnace leaking water, the typical causes will be different depending upon what season it is.

During AC or cooling season

A clogged drain line causing backup into the drain pan

If there are issues with the condensate drainage system, such as clogs or blockages in the condensate drain line, the water may back up and leak.

Frozen coils

If the evaporator coil, which is part of the air conditioner, becomes too cold due to issues such as low refrigerant levels, restricted airflow (possibly due to a dirty filter), or other malfunctions, the condensate on the coil can freeze. When the system cycles off, the frozen condensate may begin to thaw, leading to excess water that might overflow the drain pan.

During furnace or heating season

Issues with the condensate pump on high efficiency furnace

The primary function of the condensate pump is to remove the water produced during the condensation process in a high-efficiency furnace. If the pump fails to operate correctly, it can result in the accumulation of water within the furnace or the connected components.

Broken heat exchanger

A broken heat exchanger can disrupt the proper combustion process. As a result, the temperature of the exhaust gases may be too high or inconsistent, impacting the condensation process. This can lead to water not condensing as it should, potentially causing water leakage.

Clogged drain line on high efficiency furnace

The condensate drain line is responsible for carrying the condensate away from the furnace to a drain or a designated drainage system. If the drain line is clear and functioning correctly, the condensate is efficiently removed. When the condensate drain line is clogged, the water produced during the combustion process has nowhere to go. As a result, the water may accumulate in the furnace or associated components.

Failed seals behind the inducer motor (you may see rust spots on the unit)

The inducer motor is typically located near the beginning of the combustion process, and its components, including seals, are exposed to the combustion gases and condensation that occur during operation. Over time, the seals behind the inducer motor may degrade due to exposure to heat, condensation, and other environmental factors. This deterioration can lead to cracks, gaps, or complete failure of the seals. When the seals fail, combustion gases may escape from the inducer motor compartment. This can not only compromise the efficiency of the combustion process but may also lead to the release of acidic condensate into areas where it shouldn’t be.

Overheating due to a dirty filter

In high-efficiency furnaces, condensation is designed to occur, and the resulting water is supposed to be drained away. If the furnace is operating at higher temperatures due to reduced airflow caused by a dirty filter, condensation might not happen as intended, leading to potential water leakage.

If you have a standard efficiency system, it is still possible that you just have a condensation leak but would most likely be due to the exhaust or flue pipe being incorrectly sized.

Other Leaking Culprits

If your HVAC service expert determines that you do not have a condensation leak, there are a myriad of other issues that could be the cause of your furnace leaking water.

They include:

  1. Issues with your whole-house humidifier 
  2. Internal drain clog
  3. Bad secondary heat exchanger in the furnace 
  4. Air conditioner leaking

Air conditioner leaking, you say? Yes, in seasons where you may use the furnace and air conditioner it is possible that when you are using the AC your condensation pan can fill with water and drip into your heating system, making you think you have a furnace leak problem.

SEE MORE: AC repair


  1. Shut your furnace off. There should be a switch next to the furnace. If you cannot locate this switch, then turn the system off at the breaker box.
  2. Clean up all the water as best as you can and find the source of the leak. Water damage can happen quickly. This will also allow you to see if the leaking continues.
  3. Check the air filter. If the filter is dirty, then change it and see if that fixes the issue.
  4. Call a professional HVAC service company. If changing the air filter does not stop the leaking, you’ll want to schedule furnace repair service.


In short, yes. If your furnace has water on the floor around it, you want to be sure you call for furnace repair. Left without repair, the water can drip onto your circuit board, get into the blower motor and eventually cause the furnace to shut down.


Call us at Quality Comfort Home Services at 513-620-4822 if you are experiencing a furnace leak or are in need of any other furnace repair. You can also book online anytime. Our trained and certified technicians come with fully stocked vehicles, ready to fix your furnace problem. We also provide a lifetime guarantee on our repairs!