"Jim" nospam@wherever wrote in message
el...
Hello,

I just had the furnace guy refire up my energy efficient furnace as
it went out last night. We have been having a cool spell (-45 to -50
Celciuse) in Canada here... I have a 2600 sq ft four level split home and
they installed the new furnace last year and I have these three inch
plastic pipes as an intake and exhaust. Problem is the exhaust had to be
run for quite a ways (through the garage and up through the roof) for the
installation and the very top of the exaust is freezing over (The exhaust
is sloped properly and condensation does drain back) The part of the
exhaust is the verticle section coming up through the roof...The verticle
section rises about 5 feet over the roof so that it won't be buried in a
snow bank........This morning we cut two feet of length as the end of it
iced over and closed the exhaust. I don't know weather to use heat tape on
these three inch lines or just wrap with insulation.... Thoughts...typing
with gloves on here...just got things up and running again...close
call...laying in bed this morning and our cat came to bed and noticed he
was cool to the touch...LOL...lucky I didn't freeze any pipes Thanks.....
Jim


You want to do the portion above the roof only? I see at least one problem.
Plastic does not transmit heat very well and the tape may do no good at all.
Wrapped around the outside, the moisture on the inside top inch or so could
still freeze and build an ice block.

I'd consider transitioning to a copper tube (expensive as that may be) or
3" electrical conduit if you want to heat it. You may only have to heat the
top 12" or so to prevent freezing.