The furnace air intake (at left) and the exhaust (right) after being dug out of a deep snow drift.

The furnace air intake (at left) and the exhaust (right) after being dug out of a deep snow drift.


At the height of what seemed like a blizzard Saturday night a chill set in at our normally cozy farm house in western Wisconsin, where a furnace repairman would surely be hard to find. Turned out to be a fairly simple, but potentially dangerous problem: The furnace vents along the back of the house were buried in waist-deep snow.

In many houses new high-efficiency furnaces vent out the side of the building, creating a big problem during heavy snows and extended periods of extreme cold. When those vents are buried in snow they're no longer able to supply the furnace with the fresh air it needs to operate and most will automatically shut off. But not all of them, and that can create a potentially lethal situation if the exhaust vent is blocked and the furnace doesn't shut off - carbon monoxide produced by the combustion process in the furnace can fill your house. The same can be true of your water heater, which also has a vent that needs to be kept clear. So here's what you need to do:

- Keep at least a three-foot area around those vents clear and free of snow. Check it regularly to make sure that strong winds haven't caused drifiting.

- Make sure that your carbon monoxide detectors are in working order. Carbon monoxide is an extremely dangerous gas that's colorless and odorless!

- After you've cleared the vents many furnaces will automatically restart, but not all of them. Aside from hearing it trying to restart and feeling warmth from the ducts, you'll know it's working because the warm air that's removed through the exhaust vent will melt nearby snow and sometimes create little icicles. 

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