Gary, I just can't agree. There should be no water or snow infiltration in a
properly designed termination. (It has a damper in the exterior cap to
prevent just that.)

By adding unnecessary twists and turns, you are adding some back pressure
for the blower to overcome, which would degrade its performance (to whatever
extent would depend on the specific system.) Also adding a trap could
possibly cause some moisture in the air stream to condense prior to being
evacuated (this would especially true if your roof cap has no damper and
allows rail to enter). This would be undesirable as standing water could
deteriorate the vinyl ducting over time. (I prefer metal ducting as the high
heat in an attic can cause plastics to deteriorate over time).

In any case, a duct that runs as straight as possible is the most desirable
way to vent, and millions of homes exist with roof terminations where this
presents no problems at all.

"gary" wrote in message
news:j6bff.524440$1i.262605@pd7tw2no...
That is done on all new buildings here. I just took a picture of one
today. Can I upload binaries here? Do you really think a slight U in a 4"
pipe is going to fill up with water from the minimal amount of snow or
rain that might get into the pipe? If you get that much water in there
the trap is NOT your problem. You have other problems. If you do not
put the "trap" there where do you think that water goes. Right into your
fan, your motor and your grill (if metal) and causes rust.


"Dennis" wrote in message
newsP9ff.22603$5R4.2331@trnddc06...
Your kidding right? Trap the duct?

"gary" wrote in message
newslRef.522479$tl2.34263@pd7tw3no...
Use insulate flex ducting to prevent moisture condensation and put a U
in it so that any water that might get in the pipe through the top of
the vent does not drain back into your fan.