Worried about the water leaking around your furnace?

Don’t worry, we’ll help you troubleshoot the problem quickly. 

The most common causes of a leaking furnace include:

  1. A problem with the AC
  2. A clog or leak in the condensate line (condensing furnaces only)
  3. A leaking humidifier

We’ll explain each of these causes in more detail below.


Need a professional to give you an exact estimate for your furnace repair? Call Cooper Heating and Cooling. We provide quality repairs that will have your furnace heating up in no time. Schedule an appointment with the Cooper Green team today! 

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Cause #1: A problem with the AC

The indoor unit of a central air conditioner is usually located on top of the furnace. If an AC is leaking, it could appear that the leak is coming from the furnace or vice versa. Before we dive into the furnace leaking problems, we’ll first want to rule out the possibility that the AC is the cause of the leak.

Air conditioners produce condensation when warm, humid air comes into contact with the cold cooling coils inside the AC. Normally, this condensation drains into a floor drain, so you should never see pools of liquid around your air conditioner unless there’s a problem.

The most common problems that lead to leaks around the indoor AC unit include:

  • A frozen evaporator coil
  • A clogged condensate drain line
  • A cracked drain pan

How to tell if the AC is the problem: Do you notice the leaking water when your thermostat is set to COOL? If so, this usually indicates that the air conditioner is the culprit of the leaking water instead of the furnace. If your thermostat is set to HEAT and you notice leaking water, the problem is probably with the furnace (more on those problems below).

Solution: Each of the AC issues we listed above should be fixed by an HVAC technician, so you’ll want to contact a professional to inspect your air conditioner and diagnose/repair the problem.

Now let’s take a look at what causes a furnace to leak.

Cause #2: A clog or leak in the condensate line (condensing furnaces only)

As their name suggests, condensing furnaces produce condensation during the heating process. Normally, the condensation is carried out of the furnace via a plastic pipe (usually PVC) that feeds into a condensate drain. 

However, if the condensate drain or pipe is clogged, condensation can leak out of the furnace, which would explain the liquid you see pooled around the unit.

How to know if you have a condensing furnace: If you see a plastic PVC or CPVC pipe coming out of the furnace, it means you have a condensing unit.

Solution: To fix this problem, a professional must inspect the condensate drain and pipe and fix any leaks or clear any clogs. 

Cause #3: A leaking humidifier

Some homes in our area have a whole-home humidifier installed in the HVAC system to have more comfortable air during the dry winter months.

Although it is relatively uncommon for a humidifier to leak if its drain lines are clogged or internal components malfunction, it’s possible to see leaking water around the furnace.

A trained HVAC professional should inspect the humidifier and ensure it drains properly and that all connections are secure.


Ready for Your Furnace Repair? Contact the Cooper Green Team Today. 

Since 1978, we’ve helped Denver homeowners save money, help the environment and resolve their furnace, AC, and electrical problems. Our skilled technicians maintain fully-stocked trucks, so they’re always prepared to fix your furnace correctly —the first time. 

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