On Tuesday, February 2, 2010 at 3:22:41 PM UTC-7, MNRebecca wrote:
Once or twice each winter, my furnace shuts down due to a clogged air
intake pipe. The pipe clogs in subzero weather or during/after a
blizzard, presumably because of snow/ice building up inside the pipe
(said the repair guy after traveling out in a blizzard on Sunday
morning the first time it happened). If I disconnect the pipe from
the furnace and let it draw air from the room instead (which I'm told,
by the repair guy, is harmless), it fires back up and runs fine. But
I hate the idea that, each year, I have to live in dread of the time
I'll wake up in the middle of the night to a disturbingly cold house
and then have to live with a furnace drawing air from a basement room
instead of outside (until temps outside climb above freezing, which
can be weeks).

The intake and exhaust pipes (white plastic PVC pipes) vent to the
outside right next to each other, just a few inches apart, about 2.5
feet above the ground. Each bends 90 degrees in opposite
directions...the intake faces east and the exhaust faces west.

Any advice on how I can keep the intake pipe from clogging? Thanks so
much if you can help.

The exhaust should rise up 18 inches and face out with a 90 directly away from the building. This will prevent cross contamination of the exhaust gases with the return air supply to your appliance. This should reduce the likelihood of recurring events but it may not eliminate it entirely. I read about a new product which is supposed to prevent the ice or frost at the vents by a company called Frostfree venting. Their product may solve your issue.