My Furnace is Leaking Water – What Do I Do?


Water leaks in your home are frustrating, time-consuming, and can cause costly damage – not to mention costly repairs.

But what do you do when it’s your furnace leaking water? It’s easy for panic to set in – especially as the temperatures get colder and colder.

Here’s what you need to do if you find yourself in this situation.

Turn off Your Furnace and Call Dr. HVAC for Repairs

If you discover your furnace leaking water, the first thing you should do is turn it off.

First, make sure your thermostat is off. Then turn the shut-off valve, located on the gas line, connected to your furnace and the electrical breakers associated with your furnace.

The problem causing the furnace leak is likely something only an hvac professional should handle, so your next step is to call us.

You can book an appointment online or call 905-457-4425.

You should then mop up any water that’s collected around the base of your furnace. Standing water is bad for your furnace and your floor.

Remember: Only do this once your furnace electrical circuit is shut off. Then, stop kicking yourself for not installing a floor drain, and if you do have a floor drain, make sure it isn’t clogged.

If your furnace looks like a lonely island in the middle of a small pond, it’s possible to rent a wet/dry vacuum from big hardware stores to make cleanup easier.

Why Is My Furnace Leaking Water in the First Place?

Depending on whether you have a high-efficiency furnace (an AFUE rating of 90 or more) or a conventional furnace, several different things will cause a furnace leak.

1. High-Efficiency: There’s a Leak or a Clog in the Condensate Lines

High-efficiency furnaces create condensation through the heat exchange process. When operating normally, this condensation is drained safely away from your furnace through the condensate line and drain trap.

If there’s a leak or a clog in the condensate lines, you’ll quickly find a puddle around your furnace.

2. High-Efficiency: Your Condensate Pump Isn’t Working

A condensate pump is what pushes the water through the lines and away from your furnace. These can experience mechanical problems, which often cause water leaks. At times, it may stay on due to an issue with the float and check valves. It’s also possible the condensate lines were not placed properly, or buildup has caused a clogged condensate trap or condensate drain line and caused furnace leaking and causing headaches.

3. Conventional: The Metal Exhaust Pipe is Creating Condensation

If your furnace has an AFUE rating of less than 90, it’ll have a metal exhaust vent pipe (vs. the white PVC vent pipe of a high-efficiency furnace). The exhaust vent carries away the gases produced during the combustion process through the exhaust pipe and releases them outside while they’re still hot.

If this venting pipe isn’t properly sized for your furnace, gasses can get trapped by the extra air. Eventually, they cool down – this forms condensation, which leaks out of your furnace.

4. For Any Furnace: The Humidifier is Leaking

Many homeowners choose to add a built-in humidifier to their heating system to make their homes more comfortable during the dry winter months.

They have water constantly moving through them, and if they spring a leak or become clogged, it looks like it’s your furnace that’s leaking water. A humidifier leak will have its own set of fixes, but a leaking humidifier is still a water leak.

A Dr HVAC certified technician will thoroughly inspect your furnace and humidifier when diagnosing the source. We can also take a look when you have your annual furnace tune-up.

Make Sure To Replace Humidifier Pad

Your humidifier will keep working even with a clogged or dirty humidifier pad, but it definitely won’t be working very well. A whole house humidifier with a clogged pad will be a significant drain on your energy, will cause a sluggish HVAC system, and will wear out your humidifier long before its time.

A clogged or dirty humidifier pad also leads to trapped moisture causing the indoor air quality to deteriorate as it builds up with bacteria and mold growth that circulates through your home instead of clean, humid air from a well-kept machine.

5. For Any Furnace: It Might Actually Be the Air Conditioner

If we’re in that seasonal grey period where you use your air conditioner one day and turn on the heat the next, it may not be your furnace leaking water.

Air-conditioners absorb a lot of moisture from the air inside your home, so they also have condensate lines and an internal drain system that empties into a drain pan. So if there’s a clog or water leak, or the condensation pan fills and overflows, it could appear as though your furnace is the source when it’s the condensation leak.

6. For Any Furnace: Heat Exchanger Problem

Heat exchangers are an essential part of your furnace and the combustion process. It is a metal shield that prevents the exhaust gases produced during the combustion process from entering your ductwork with the warm air. When the heat exchanger heats up, the metal expands and cools and contracts back to the shape it held when it was at room temperature. Unfortunately, after years of this process, it is not uncommon for the furnace to fail and leave you with a cracked heat exchanger. If the heat exchanger cracks, it can lead to life-threatening carbon monoxide circulating in the home’s air.

There is also a secondary heat exchanger on models where water is changed from a vapour to a liquid to release more heat into the secondary heat exchanger. This feature is typically found on high efficiency furnaces as it provides more heat for the same amount of gas. By comparison, a standard efficiency furnace will have only one heat exchanger. A secondary heat exchanger will need just as much routine maintenance, which doesn’t make them less susceptible to water leaking.

7. For Any Furnace: Dirty Furnace Filter

A leaking furnace should not be your only motivator to replace your filter. A dirty furnace can restrict airflow, which causes your furnace to overwork and subsequently overheat. Eventually, this causes the breakdown of your furnace system altogether, which obviously is an expensive problem to fix. Replacing the filter is a relatively simple, inexpensive fix though it can be easy to forget about maintenance with your busy schedule. We recommend setting a filter replacement reminder on your calendar every 90 days, so you don’t forget!

Make Sure to Replace Your Furnace Filter

As a rule, you should change your furnace filter every 90 days. But if your furnace is leaking water, you should swap out the filter after it’s repaired and before you turn your furnace back on. You may notice your furnace blowing cold air or shutting on and off as a result.

A wet, dirty, or clogged filter will restrict airflow and put extra strain on your furnace. It’s best to start fresh with a new/cleaned filter.

Make Sure To Keep Your Furnace Well Maintained

When you notice water leaking is not the time to think about your furnace upkeep. At least annual maintenance at a minimum is the way to make sure you don’t end up in a bad situation. Having a certified technician look at your furnace regularly will ensure you know if any parts need replacing. To prevent furnace water leaks, parts that may need replacing are the flue pipe, drain line, water lines, furnace coil, and the other essentials that keep your HVAC system running smoothly.

We’ll Find the Source of the Leak and Get Your Heat Back in No Time

No matter what make or model of furnace you have, we can make the necessary repairs.

Our team of technicians are highly-trained and professional, able to diagnose the problem and have you up and running again as quickly as possible.

Learn More About Dr. HVAC’s Repair Services