Why Is My Furnace Leaking Water, and What Should I Do? A Barrie Guide

Water around a furnace usually comes from the drain system of a high-efficiency furnace, a humidifier attached to the ductwork, or something nearby, like a water heater or plumbing. A leak can also stop the furnace from heating. Start by finding where the water is and keeping it away from anything electrical. Then mop up, protect your belongings and call. Don't open the furnace to look inside.

Safety first: If a CO alarm goes off, leave the home now and call 911 from outside. If you smell gas, leave and, from outside, call 911 and Enbridge Gas's emergency line at 1-866-763-5427. On propane, call 911 and your propane supplier. Don't stop to mop up or check the furnace.

Where is the water around my furnace coming from?

Look at where the water sits and what's above it. A puddle at the base or front of a high-efficiency furnace often points to its drain system. Water running down the ductwork above the furnace can come from a whole-house humidifier. In summer, the air conditioner coil above the furnace can drip too. A puddle with nothing dripping above it may come from a water heater, a pipe, a floor drain or the foundation.

What to look at, without opening anything

• The furnace base and front: is the water coming from under the furnace, or running toward it?
• The ductwork above: are there drips or water stains on the metal?
• The small plastic tubes and any small pump box beside the furnace: are they wet on the outside?
• The water heater, pipes and floor drain nearby: is the water closer to one of those?
• The filter: if it slides into a slot outside the furnace, check whether it looks wet. If the filter sits behind a furnace door, leave it.

Is it normal for a furnace to make water?

Yes, for a high-efficiency furnace. It pulls so much heat from its exhaust that water vapour turns into liquid, called condensate. That water is supposed to flow through plastic tubing to a floor drain or a small pump, not onto the floor. An older furnace with a metal vent pipe shouldn't make water you can see, so water there is a sign to call.

How to tell which furnace you have

• High-efficiency: usually two plastic pipes run from the furnace to an outside wall or the roof.
• Older or mid-efficiency: a metal pipe usually runs from the furnace into a chimney or a roof vent.

Natural Resources Canada describes condensing furnaces as sending this water to a floor drain or a condensate pump. Some condensing furnaces also share a drain with a central air conditioner or a humidifier, so one blocked drain can affect more than one system.

Can a water leak stop my furnace from heating?

It can. When water from a high-efficiency furnace can't drain away, it can back up inside the furnace. On many furnaces, a safety switch then stops the burners, so the furnace shuts off or won't start. You might see a puddle, a flashing status light and a cold house all at once.

Signs the leak and the lost heat are linked

• The water appeared around the same time the heat stopped.
• The furnace starts, runs for a short time and shuts off. Our guide to a furnace that turns on and off covers that pattern.
• The puddle grows while the furnace tries to run.

Don't keep restarting a furnace that's sitting in water or leaking. Each restart can add more water.

What should I do first when I find water by the furnace?

Check the safety basics, then protect your home. If the water is spreading near outlets or the electrical panel, stay out of the area and call your local electric utility. If the floor around the furnace switch is dry, turn the furnace off at that switch. Then mop up what you can safely reach, move belongings away and call for help.

Step by step

1. Stay safe: don't stand in water to reach the furnace switch, and don't touch anything electrical with wet hands.
2. Turn the furnace off: only at its switch, and only if the switch and the floor around it are dry.
3. Mop up: use towels, a mop or a wet/dry vacuum on the floor around the furnace, not inside it.
4. Protect belongings: move boxes, rugs and stored items off the wet floor.
5. Note what you saw: take a photo, and note where the water was, roughly how much, whether the furnace was running and when the heat stopped.
6. Call: Furnace Repair Barrie answers 24/7 at (249) 209-2216.

Ontario's Electrical Safety Authority warns that electricity can move through water or wet flooring. Its flood safety guidance says not to enter a basement if water is above the level of outlets, baseboard heaters or the furnace, or is near the electrical panel. In that case, call your local electric utility to disconnect power. Guidance can change, so check the current page.

When is a furnace leak urgent enough to call right away?

Call right away when water is near electrical parts, the puddle keeps growing, or the leak has stopped the heat in freezing weather. A slow drip with the heat still working is less urgent, but it still needs a look soon, because water damage and mould can build quietly.

Call now if

• The puddle is growing or spreading to finished areas.
• The furnace has stopped heating and it's below freezing outside.
• Water is dripping from the metal vent pipe of an older furnace.
• Someone at home is vulnerable to cold.

Our guide to whether a broken furnace is an emergency can help you weigh the timing. Our emergency furnace repair page explains what happens when you call.

Why does my furnace only leak during a cold snap?

The drain line may be freezing. Some condensate lines run through a garage, crawl space or outside wall, or drain outdoors. In a deep freeze, water in those lines can turn to ice and block the drain, so condensate backs up and spills near the furnace. Some furnace installation manuals warn that a frozen drain can crack and cause water damage. Barrie's long, cold winters make this worth checking with someone who works on furnaces. When you call, mention whether the leak started in very cold weather and whether the line runs through an unheated space. Don't use heat on the line, and don't move or disconnect the tubing yourself.

What if the filter or the area near the furnace is wet?

A wet filter, or damp spots away from the furnace base, usually means water is getting onto or into the furnace from above or inside. Likely sources are a humidifier, the air conditioner coil or a backup inside the furnace. If the filter is soaked, turn the furnace off at its switch from a dry floor and call. A soaked filter can restrict airflow and grow mould.

Once the leak is fixed, replace a filter that got wet. Our guide to how a dirty furnace filter can stop the heat explains how to change one safely.