In the middle of a cold and snowy winter day, the last thing you want is for your furnace to stop heating your home. Within the past couple of weeks, you may have noticed plenty of social media posts warning you to clear your furnace vents of snow. But what does this mean? No, it does not mean you need a duct cleaning!

During extreme winter weather events (i.e. heavy snowfall and extreme cold), your furnace and water heater exhaust vents may become blocked with snow, ice, or frost. New models of furnaces are factory programmed to automatically shut off when Carbon Monoxide (CO) levels are higher than usual within your home, and for a good reason. Without proper ventilation, carbon monoxide can build up inside your home and the consequences can be fatal. The burning of natural gas produces both water and CO. Where do these gases go? Furnace exhaust gases are vented outside via a PVC pipe and are typically one to two feet above grade.

If you notice your furnace is not properly heating your home, check to ensure your exhaust vents are clear of any obstructions. Even if your furnace is running, there is a possibility that the exhaust vent could be partially blocked. Over the cold winter months, frost can build up slowly in and around the vent, reducing your furnace’s efficiency. So whether it’s for optimal efficiency or protection from carbon monoxide, it’s important to keep your exhaust vents clear. Here’s what to look for:

Clearing Snow

Check on your furnace vent during and after heavy snowfalls, and clear snow away from the vent’s opening if it builds up. If you notice a mound of snow blocking your furnace vent, clear it out by hand – don’t use a shovel or a snowblower, as either could cause damage to the furnace vent pipe.

Dealing With Frost & Ice

If the outside temperature remains below freezing for a few days in a row, it is a good idea to inspect your furnace exhaust vent. If you find a thin layer of frost on the exhaust pipe, you can scrape it off with a plastic putty knife. Next, take a look in the exhaust pipe vent to see if there is still any further buildup.

If there is a heavy frost buildup, you will need a heat source to melt the ice. One way is to plug a hairdryer into an outdoor extension cord. Turn the hairdryer to its highest setting and use the hot air to melt frost inside the pipe. Remember to keep your hands safe and wear protective gloves while using the hairdryer.

While the hairdryer is a handy tool for clearing frost, don’t ever use it in the rain or during a snowfall, as it poses a risk for electrocution.

Restarting Your Furnace 

If your furnace shuts off due to a blocked exhaust vent, restart it according to the manufacturer’s instructions after you have dealt with the blockage.

If you are having issues restarting your furnace, call an expert from Climate Works, and we will be happy to assist you.

You should check your exterior exhaust vent throughout the winter months, especially after a new snowfall.


Often referred to as the “silent killer,” CO is an invisible, tasteless and odourless gas that can cause severe illness or death. The poisonous gas is produced when fuels, such as propane, gasoline, natural gas, heating oil or wood do not burn completely in fuel-burning appliances, such as furnaces, fireplaces, hot water heaters, stoves, barbecues, portable heaters and generators, or vehicles.

There are more than 300 CO-related deaths per year and more than 200 hospitalizations per year in Canada. While it is mandatory to have carbon monoxide detectors in all homes now, they are not 100% reliable (they become unplugged, run out of battery, may not be in the right room, etc.). This is why you need to take every step to ensure your furnace vents properly.

Exposure to CO can cause flu-like symptoms, such as headaches, nausea and dizziness, burning eyes, confusion, drowsiness and loss of consciousness. If you or others in your household or building have these symptoms, go outdoors and call 911 immediately. If your CO alarm sounds and no one is suffering from symptoms of CO poisoning, check to see if the battery needs replacing or if the alarm has reached its “end-of-life” before calling 911.