On Mon, 28 Jan 2013 09:20:48 -0500, Jim Elbrecht
wrote:

" wrote:
-snip-

I don't know about the radon vent, but I found it very
curious that the install manual for my Rheem condensing
furnace says that you can't put ANYTHING over the
2" vent pipes that extend outside. Apparently the concern
is the effect George described, ie snow/ice freezing up
over any screening. The obvious downside is that there
is a free and open route into either the exhaust or intake.
The latter would allow a rodent into the unit compartment
with the wiring, gas valve, etc. It would seem to me the
risk of something bad happening, including blocking the
vents without some kind of screen, is at least as great as the snow
problem.

With the furnace it makes sense, as that is an intermittent airflow
[and very moist airflow, to boot] . But am I behind the times
thinking a radon vent runs 24/7?

You're right but there isn't much air flow. The idea is to pull a
vacuum under the slab so any radon under the slab will be pulled out.
I'm not sure there would ever be enough moisture to cause a problem,
though.