ice build up

What to Do if Ice Forms Around Your Furnace or Power-Vented Water Heating Appliance Vents

No one likes it when we get extended cold snaps of -20°C temperatures. Luckily you have your furnace and hot water heaters to keep things comfortable.

However, during extreme cold periods, ice pillars can build up underneath the exhaust for your furnacepower-vented hot water tanks or high-efficiency on-demand water heater.

In most instances, it’s harmless. But in some cases, if ice builds up and freezes over the exhaust vent, it can stop your gas appliance from working.

What causes the ice buildup?

In Calgary, furnaces and hot water heaters burn natural gas to create heat. The exhaust gases exit through vents, usually on the side of your home (or through the roof).

On extremely cold days, the warm, moist air in the exhaust will freeze when it comes into contact with the blast of cold air. This can cause either a large cone of ice to grow under the vent (forming from the ground up) or the accumulation of hoar frost within the furnace, hot water tanks, or on-demand water heater intakes, as the moist air draws in.

While it looks serious, it is generally harmless.

When IS ice formation a concern?

This can pose a problem if the damp exhaust is drawn back into the appliance’s fresh air intake vent and freezes. This can cause a frost buildup large enough to block the whole intake.

If this happens, the furnace, power-vented water heater or on-demand water heater will automatically shut down… leaving your home without heat or hot water.

An even less common issue involves the exhaust vent freezing. This can occur due to faulty installation. For example, if the exhaust is too close to the ground (less than 18”), is positioned in the wrong direction, or is obstructed by an air conditioner fence or another object.

When should you call a professional?

In most cases, a blockage will cause your furnace to shut off. If this happens, the furnace has safety switches that will stop it from running. You should still call a repair company.

In cases where the exhaust is frozen, you’ll have solid ice along the entire length of the pipe that is sticking outside. It is generally best to have a professional clear it. DO NOT try to remove the ice blockage yourself. You may risk damaging the exhaust port. The furnace technician will need to reroute the exhaust to prevent this from happening again.

If the intake is blocked with frost/ snow/ ice, it can generally be cleared by reaching in with your fingers and removing any snow or loose ice. One trick is to gently tap the side of the intake pipe with a broom handle to loosen things up.

Once the blockage has been removed, the furnace technician will restart your furnace and ensure everything is running properly.

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What does it cost to inspect and repair a blocked appliance exhaust?

At Advanpro, we will send a technician to investigate the problem. The visit will involve a standard callout fee of $99 (plus GST). Clearing the blockage will generally require an hour of labour (billed at $109/hour).

If the vent was improperly installed and requires reconfiguration, an estimate for parts and labour will be provided by the onsite technician. If you approve the quote, the repair can be done immediately. On average, the quote will come in between $100 and $300.

Note: If you require an appointment outside of regular office hours an emergency service fee will apply.

Keep an eye on your vents during cold snaps

When the temperature plummets, the last thing you want to fail is your furnace. After a few days of extreme cold, put on your parka and take a quick peek at the exhaust pipes to look for blockages. If you are away, it doesn’t hurt to have a neighbour take a look, so you don’t come back to a frozen home!

At Advanpro, we’re committed to helping Calgarians keep warm and stay informed.

What to do if ice builds up around the appliance events outside your home in extreme cold:

  1. Go to the side of your house to take a look. Be careful. It might be slippery.
  2. Check that the ice isn’t physically blocking the exhaust or intake opening. If not, there is no cause for concern.
  3. Determine what is blocked.
    1. Exhaust Port: Call a furnace professional. Don’t try removing yourself.
    2. Intake Pipe: Try to clear any blockage by hand.
  4. Your furnace should restart once the blockage is removed (after 3-5 minutes). If not, you can reset the power to the furnace to get it to attempt to recycle.
  5. If the blockage was in the exhaust vent, a technician should reroute the pipe to prevent it from happening again.


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