Snow Drifts and Carbon Monoxide

Watch out for Drifting Snow covering your gas or propane fueled furnace's exhaust vent.
There are reports everywhere from New York to Massachusetts to Arizona about Carbon Monoxide poisonings caused by snow blocking  furnace exhaust vents.  There can be similar problems with gas clothes dryer vents, gas water heater vents, area heater stoves, pretty much any appliance that uses a flame to produce heat.
This isn't a new thing.  Boston problems were in the news in 2006.  Blocked exhaust vents have always been a potential problem.  It's just that old style furnaces had "smoke stack" like vent flues on the roof while new high efficiency furnaces might just have a PVC pipe run out the sidewall of the house or foundation.  It's always been possible for a vent to get clogged up with a bird's nest, or insects like wasps.  But now it can be ground dwellers like mice or rabbits too.  Garden plants, weeds, grasses, all kinds of things can grow up into the turned down rainhood of a vent.  Even piles of leaves or mulch.

Notes to the DIYers out there:  When installing a gas appliance exhaust vent,
Keep it up off the ground to avoid debris piled against it. 
Don't caulk the opening closed.  Caulk around it, but don't seal it shut.
Don't use the vent as a sleeve to run a garden hose out to the yard through.
Don't turn the end of the vent "up" to catch rain water for the humidifier.
Don't use the warm vent air to heat the dog's house.
Don't combine HVAC vent with plumbing vent - not even if the furnace vent pvc pipe does look just like the sink vent pvc pipe.
Don't cut the end of the vent off, not even to keep it from sticking out away from the wall.  If you hit the end of the vent with the mower or break it off accidentally, replace it properly.

Problems are Compounded by the weather; more places are getting snow drifts this winter that usually don't have any drifts at all for years at a time.  Added to that is the trend for more people to move around between regions of the US (or the world for that matter).  Your new neighbor that grew up in Louisiana may have never had to deal with a 3' snow drift.  And finally, more people than ever before are renting instead of homeowning.  A renter may not know who's responsibility it is to keep the snow drift off the balcony of the apartment.

On the other hand, if you have an all electric house with an electric furnace, it probably doesn't produce Carbon Monoxide.  But, yes, a gas furnace does often use electricity for the fan, thermostat, and igniters.