How to avoid ice-clogged furnace air intake pipe?

 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.

  On Tue, 2 Feb 2010 14:22:41 -0800 (PST), MNRebecca


It sounds like your flue is tilted back towards the house so the
condensate runs back to a low spot and freezes.  If this is the
problem, you should put a pretty good pitch on it so all condensate
runs out of the pipe before it can freeze.  Another possibility is
that the flue is too long causing a similar problem (freezing before
running out of the pipe).  In either case the fix shouldn't be too
complicated. If you can't change the pipe slope or length, perhaps
some insulation is in order.

 
Ummmm.....no, it doesn't sound like that at all, actually. Flue != intake.

 On Wed, 03 Feb 2010 00:12:45 GMT, spambait@milmac.com (Doug Miller)
wrote:


Good point.  I'd seen the issue with flues before.

 MNRebecca wrote:


I suspect rain and/or snow are blowing (or being sucked) into the
intake at times, along with moist exhaust air.  I'd put an extension on
one or both to move the openings further away, then possibly put
another elbow on the intake so it points downward.

Another approach would be to add a "dorade box" (used for on-deck air
vents on sailboats to prevent water from entering) over the intake
pipe.  Build a simple wooden box around the pipe end (which points
sideways or upward), attached/sealed to the house, with an opening in
ther bottom of the box.  Leave enough room inside the box for free
airflow through it.