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The Impact of Snow on Your Furnace

10/01/2006

When winter comes and the snow piles up, getting our cars and walkways shoveled out is always our first priority. I'd like to present you with a new first priority: making sure your furnace exhaust pipe is clear.

Newer High Efficiency Furnaces

Houses with newer high efficiency furnaces don't need the rooftop chimneys we're used to seeing because their high efficient design results in low flue temperatures. Instead, they can vent out the side of your house through plastic PVC pipe. Some of these furnaces also use a similar pipe to draw in combustion air for the furnace. If snow is allowed to accumulate too high in front of these pipes and cover them, you could face a couple different scenarios. One is that the combustion gases can not escape to the outside because the exhaust pipe is covered with snow. In this potentially hazardous scenario, the gases which can contain harmful and potentially lethal levels of carbon monoxide (CO) back up into your furnace and into your house. Excessive levels of CO have been known to cause flu-like symptoms and in extreme cases, death.

A second scenario is a snow clogged combustion air intake pipe. If this pipe becomes clogged, your furnace will not be able to draw combustion air to to the combustion chamber and your furnace will shut down. No flames = no heat and a cold house.

Most houses with standard mid efficient furnaces vent combustion gases to the outside through rooftop chimneys but draw their combustion air from the square footage inside your house. These furnace/chimney setups normally don't face the snow-related problems mentioned above due to being situated on your rooftop. However, it doesn't make them immune to the backup of CO into your house. Rooftop chimneys should be properly capped with a rain hood / cage. The hood will help prevent water and snow from getting into your chimney and the cage will prevent animals from finding their way in and clogging your flue. More than one house has filled up with CO fumes due to a squirrel that lost its footing.

If you have any appliances in your house that burn fossil fuels (gas, oil, coal), you should have at least one carbon monoxide detector, preferably one for every floor. CO is a colorless, odorless gas that is poisonous to all of us. We have a CO detector in our basement that alerted me to a growing problem with CO buildup in my own house. I religiously press the test button of the unit every day to see if any levels of CO are present. One day, I pressed the button and it displayed a reading of over 100 (124 to be exact)!!! I looked at the scale for CO levels on the monitor and the recommendation for levels of 100+ was to evacuate the house. Being the stubborn and foolish type I that am, I remained in the house trying to locate the source (I do not recommend this for anybody). We don't have gas heat or appliances and the only fossil fuel burner we have in our house is the oil-fired furnace. I shut the furnace down and removed the flue exhaust pipe to find the opening inside the pipe nearly clogged shut by deteriorated brick and mortar within the chimney flue. The good news is we got to live to tell about it and you get to learn from my experience.