Yes. A high-efficiency furnace pulls in outdoor air and pushes its exhaust out through plastic pipes on an outside wall. After heavy snow in Barrie, those pipes can get buried or iced over. When that happens, a safety switch stops the furnace and the house starts to cool. If you can reach the pipes from the ground, gently brushing them clear often lets it run again. If it doesn't, or a carbon monoxide alarm sounds, the next steps are different.
Safety first: If a CO alarm goes off, you smell exhaust fumes indoors, or people at home feel dizzy, sick or unusually drowsy, 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 stay inside to check the vents or the furnace.
How does a blocked vent pipe stop my furnace?
Your furnace needs a clear path for air in and exhaust out. Before it lights, a small fan starts and a pressure switch checks that air is moving through the pipes. If snow or ice blocks either pipe, the switch can't confirm it, so the furnace won't light or shuts off partway through. That's a safety feature. It keeps exhaust from backing up into your home.
What you might notice
- A small fan starts, then stops, with no flame
- The furnace runs briefly, then shuts off again and again
- No heat right after a storm, heavy drifting or a deep freeze
A snow-blocked vent is one cause of no heat that you can often fix from outside. If the status light is flashing, our guide to furnace blinking light codes explains how to read and record it.
Where are my furnace vent pipes outside?
Most high-efficiency furnaces have two plastic pipes, often white, coming out through an outside wall. One brings in fresh air for burning, and the other carries the exhaust out. Some homes have a single wider fitting with both pipes inside it, and some pipes go up through the roof instead. On a cold day, the exhaust pipe often puffs out what looks like steam while the furnace runs.
How to find them
- Find the furnace in your basement or utility room, and note which outside wall it's closest to.
- Look along that wall, fairly low, for two pipe ends or one round cap.
- Check side yards and behind decks and shrubs.
- If the pipes go through the roof, don't climb up. Call instead.
How do I clear snow and ice from furnace vent pipes safely?
Only clear pipes you can reach while standing on the ground. Use your gloved hands or a soft brush or broom, and gently clear loose snow from both pipe openings and the area around them. Enbridge Gas recommends clearing appliance vents this way after every storm. Never chip, scrape, kick or hit the pipes, because plastic gets brittle in the cold and can crack. Don't shovel or blow snow toward them. If hard ice has sealed an opening and won't brush away, leave it alone and call. Never use a ladder to reach vent pipes.
Do
- Clear both pipe ends, not just the one that's steaming.
- Clear the snow below and around the pipes, so the next drift doesn't bury them.
- Look for icicles or a dripping eavestrough above the pipes. Dripping water can freeze on the openings.
Don't
- Don't use a shovel, ice pick, scraper or snowblower near the pipes.
- Don't pour hot water on the ice, or use a torch, heat gun or hair dryer.
- Don't reach into the pipes, pull them out or take anything apart.
What should I do once the vent pipes are clear?
Give the furnace a few minutes. Some furnaces try to start again on their own, but after several failed starts many wait a while before trying again. If yours stays off, reset it once: turn the furnace switch off, wait a minute, then turn it back on. If it still won't run, or it shuts off again, leave it off and call.
After the reset
- Listen for the small fan, then the burners lighting.
- Check for warm air from the indoor vents within a few minutes.
- If the furnace stops again, don't keep resetting it. Repeated resets can hide a different problem.
If the small fan runs but no flame follows, see why a furnace won't ignite.
Can a blocked furnace vent cause carbon monoxide in my home?
It can. Carbon monoxide is a gas you can't see, smell or taste, and it's made when fuel doesn't burn completely. Enbridge Gas warns that blocked appliance vents can cause malfunctions that let CO into the home. A furnace's safety switches are designed to shut it down, but they don't replace a working CO alarm.
If a CO alarm sounds
- Get everyone, including pets, out of the home right away.
- From outside, call 911.
- Don't stay inside to open windows or turn off the furnace, and don't stop to clear the vents.
- Don't go back in until emergency responders say it's safe.
Headaches, nausea, dizziness, confusion and drowsiness can be signs of CO exposure. Ontario's Fire Code requires CO alarms outside each sleeping area in homes with a fuel-burning appliance, a fireplace or an attached garage. As of January 1, 2026, the rule also covers every storey of the home. Requirements can change, so Ontario's carbon monoxide safety page has the current rules.
Why do my furnace vents keep blocking up?
It usually comes down to where snow and water collect. Drifting snow and snow sliding off the roof can bury the pipes again after a storm. In deep cold, moisture in the exhaust can also freeze into frost or ice at the end of the pipe. If the pipes block up often, ice forms inside them, or they sit close to the ground, have the venting looked at.
When you call, mention how often the pipes block, in what weather, and whether it's loose snow, frost or solid ice. Moving the pipes or adding anything to them is work for someone who works on furnaces.
How can I keep furnace vents clear through a Barrie winter?
Make the pipes part of your snow-clearing routine. In the snowbelt north and west of Barrie, and wherever wind off Lake Simcoe drifts snow, pipes can be buried overnight, so check them after heavy snow, high wind or a deep freeze, not just after big storms.
Before the snow flies
- Show everyone who clears snow at your home, including a plow or snow-removal service, where the pipes are, and ask them not to pile or blow snow against that wall.
- If you'll be away, ask someone to check the pipes and the indoor temperature.
When should I call instead of clearing the vents myself?
Call when you can't reach the pipes safely, the ice won't brush away, a pipe looks damaged, or the furnace still won't run once the pipes are clear. Call right away if the house is getting cold in freezing weather or anyone at home is vulnerable to cold. Furnace Repair Barrie answers 24/7 at (249) 209-2216.
Call now if
- The pipes are on the roof or out of reach from the ground
- A pipe is cracked, crushed, pulled loose or sagging
- The indoor temperature keeps falling
If the house is getting cold while you wait, our no-heat guide for Barrie homes covers keeping people and pipes warm. Our emergency furnace repair page explains what happens when you call.