Why Is My Furnace Leaking Water?

A leaking furnace can stem from numerous reasons. Still, the most common include a failing condensate pump, a clogged drain line, loose drain lines, a leaking whole-home humidifier, or a deeper issue within your high-efficiency furnace.

If your home is equipped with an air conditioner, the water leakage may actually stem from its evaporator coil, instead of the furnace itself. Regardless, any water leaking around your furnace should be inspected as soon as possible to prevent damage to your equipment and other safety issues.

Even a small amount of water near your furnace should be inspected immediately. While some leaks may be caused by drainage issues, other underlying causes could suggest there's an issue with your heating system or another HVAC system nearby.

Limit Water Damage

Any amount of water can cause water damage to your home, from soaked flooring and drywall to mould growth. Acting quickly can help minimize potential damage while the root cause of the leak is discovered.

Protect Electrical Components

Furnace systems rely on electrical controls, circuit control boards, blower motors, and safety switches. If water comes into contact with any of these components, it can impact the system's ability to operate correctly and damage these devices.

Restore Reliable Heating

Most high-efficiency furnaces feature safety controls designed to shut down the system if the condensate created during the heating process is unable to drain properly. This can interrupt the furnace's heating process, leaving your home without heat during those cold southern Ontario winter months.

Identify the Correct Source

Water pooling around your furnace doesn't necessarily mean that it's leaking. The source of the leak could be your air conditioner, whole-home humidifier, nearby plumbing, your water heater, or a flood drain depending on the time of year. Identifying when the water appears can help you narrow down where it's coming from.

Know When to Call a Professional

Homeowners can take note of where the water leak is collecting. But diagnosing internal electrical components, drainage systems, venting, gas, combustion components, and other internal controls should be left to certified HVAC technicians.

Finding water leaking around your furnace can be a cause for concern. By following these steps, you can protect your home and your heating system while waiting for a licensed technician to arrive at your home:

1. Turn the thermostat off to prevent the heating or cooling cycle from continuing.

2. Disconnect power if it is safe to do so without stepping into any of the pooled water or touching electrical equipment that may be wet.

3. Move belongings away from the leak to prevent water damage.

4. Absorb visible standing water with a towel to avoid contact with electrical components.

5. Look for the source without removing furnace panels and take note of where the water appears to be coming from.

6. Record when the leak occurs, such as when the humidifier was operating, or when your furnace or air conditioning was running through its cycle.

7. Take photographs of the leak and the area to help HVAC technicians quickly diagnose the problem.

8. Call a qualified HVAC technician to inspect and repair your unit.

Water leaks around your furnace don't always mean that your heating system is the source of the leak. If your home has a dedicated utility room or closet, there may also be an air conditioner, humidifier, water heater, and other mechanical equipment housed alongside your furnace.

That's why it's important to determine whether the water appears during the heating, cooling, or humidifying process, or when no HVAC system is operating, to help you narrow down the root cause before a technician arrives at your home.

Water Appears While the Furnace Is Heating

If the water leak appears when your furnace is operating, it could be due to the condensate system. High-efficiency furnaces produce condensation during the heating cycle. That water should drain properly through a condensate trap, a drain line, a condensate pump, or a floor drain.

However, if the drainage system is blocked, frozen, or damaged, water can back up and leak onto your flooring.

Water Appears While the Air Conditioner Is Running

In some homes, the indoor evaporator coil for air conditioning systems can be installed directly near or above the furnace. As warm air passes over the cold evaporator coil, condensation develops and drains through the condensate pan and drain line. If the drain line is clogged, the drain pan is cracked, or the evaporator coil freezes, water can overflow and leak around your furnace.

Water Appears While the Humidifier Is Running

A whole-home humidifier may also be the culprit for water leakage around your furnace, as these appliances are often installed directly beside furnaces in homes. Possible causes for leaking humidifiers include loose water-supply lines, damaged water panels, a blocked humidifier drain, or a leaking valve.

Water Appears When No HVAC Equipment Is Running

If water appears when none of your HVAC systems are operating, the source may stem from your plumbing, water heater, a nearby utility sink, washing machine, or floor drain.

As briefly mentioned, high-efficiency furnaces are designed to produce water when operating. Unlike non-condensing furnaces, high-efficiency furnaces remove additional heat from combustion gases. When the gas cools, the water vapour condenses into a liquid form. This condensation is then collected and transferred to the drainage system.

Water leakage occurs for several reasons, including the following:

Clogged Condensate Drain Line

Dirt, sediment buildup, and other debris can restrict the flow of water through the furnace system, preventing it from draining properly.

Blocked or Damaged Condensate Trap

The condensate trap helps water drain correctly while maintaining correct pressure levels in the furnace. When the trap is blocked or damaged, the water won't be able to drain correctly, causing it to back up into the furnace.

Failed Condensate Pump

If your furnace has a condensate pump, its job is to move the water to a nearby drain. If the condensate pump stops working, the water can overflow and collect around the furnace.
Loose, Cracked, or Disconnected Drain Tubing

As your furnace ages, the condensate tubing can deteriorate. If the hose develops a crack or other forms of damage, the water may leak through it before it has a chance to reach the drain.

Frozen Condensate Drain Line

Canadian winters are harsh. And sometimes, when outdoor temperatures drop below freezing, it can cause the condensate drain lines to freeze as well if they are routed through unheated areas of your home.

Whole-Home Humidifier Leak

A whole-home humidifier installed by your furnace can also be responsible for leaking water due to blocked drain lines, leaking valves, or loose connections.
Air-Conditioner Drain or Evaporator-Coil Problem

If you notice water leaking around your furnace during the summertime, it could be due to your air conditioner. This often stems from a cracked drain pan, dirty air filters, a clogged condensate drain, or a condensate pump issue.

Dirty or Severely Restricted Air Filter

A clogged air filter won't cause your furnace to leak, but it can contribute to water leaking around your furnace during the summer, as restricted airflow can cause the indoor evaporator coil of your air conditioning system to freeze. As the ice melts, the excess water may overflow and collect around your furnace.
Internal Collector Box or Secondary Heat-Exchanger Problem

High-efficiency furnaces have numerous condensate parts, including a collector box, drain hoses, and heat exchangers. If one of the components is damaged and develops a leak, water can escape and pool on the floor.

Nearby Plumbing or Appliance Leak

The water leak may also stem from another appliance around your furnace, whether it be a water heater, washing machine, utility sink, or sump pump.

Small amounts of condensation aren't a cause for concern. But water around your furnace should always be treated seriously, especially if the water is pooled near electrical components.

Call for Urgent Help When

• Water is touching electrical components.

• The furnace repeatedly shuts down.

• The leak is active and cannot be stopped.

• Water is entering the furnace cabinet.

• Rust, soot, scorching, or unusual discolouration is visible.

• The furnace makes unusual sounds.

• A burning or electrical smell is present.

• A natural gas odour is present.

• A carbon monoxide alarm sounds.

• Occupants experience headache, dizziness, nausea, confusion, weakness, or shortness of breath.

Furnace repairs should be conducted by certified technicians. However, there are a couple of checks homeowners can make before scheduling a repair appointment:

• Thermostat settings (heating or cooling mode)

• Which HVAC system was operating when the leak appeared

• Whether water is clear or contains debris

• Whether the drain hose is disconnected

• Whether condensate pump reservoir is overflowing

• Whether furnace filter is dirty

• Whether another nearby appliance is leaking

• Whether condensate drain is blocked by snow or ice outdoors

• Whether or not the leak stops after the HVAC system is off

Note that you should avoid all electrical components, refrigerant lines, and gas components.

During your appointment, an HVAC technician will likely inspect the following:

• Furnace type and efficiency

• Condensate drain tubing

• Drain-line slope

• Condensate trap

• Condensate pump

• Pump float and safety switch

• Collector box

• Internal drain hoses

• Secondary heat exchanger

• Intake and exhaust venting

• Furnace pressure switches

• Whole-home humidifier

• Evaporator coil

• AC drain pan

• Air filter

• Blower operation

• Refrigerant system, when applicable

• Floor drain and discharge location

• Electrical components exposed to moisture

• Rust or corrosion

• Error codes and shutdown history

To prevent future water leaks, homeowners should aim to do the following:

• Schedule regular maintenance appointments with a professional technician once a year

• Replace air filters as recommended by your manufacturer

• Keep your mechanical room or closet free of clutter

• Have your humidifier serviced once a year

• Protect condensate lines from freezing by improving insulation throughout your home

• Test carbon monoxide alarms every month to ensure proper operation