In areas where it is very cold and the
pipe passes through an unheated
attic, condensation (or ice) can form on
the inside of the pipe. This happens
because the flap at the fan doesn't
usually close 100% and allows some
inside air to pass even when the fan is
off. If ice forms, it will eventually
melt and might probably drip from the
fan. I've had it happen.
Why not use the pre-insulated flexible duct? The big box stores around
here all carry it. Unless your run is really long, the extra losses
won't be an issue on the push side of the fan, and it will be quieter.
I worked for a manufacturers rep many years ago. One of the lines we carried
was pipe insulation in sizes from 1/2" to 12" with various types of insulating
material and several different sheaths.
If you contact
Accessible Products Co.
2122 W 5th Place
Tempe, AZ 85281
Phone: (480) 967-8888
Toll Free: (800) 922-5252
Fax: (480) 894-6255
they may be able to give you the name of their representative/distributor in
No, I have nothing to do with Accessible Products anymore.
New Eagle, PA
I don't know the specifics of your installation, but if at all possible,
try to slope the majority of the line towards the outside vent. That allows
any condensation that builds up to drain off outside the building and not
back into your fan.
As for the insulation, I just put an extra layer of fiberglass batts over
my vent lines in the attic space (ours vent out the gable end walls).
They're probably better insulated than the rest of our house. :)
You could also wrap the pipe with fiberglass batts and use string, duct
tape, plastic zip ties, or something similar to hold it all in place.
Alternatively, use long strips of insulation, and start wrapping at one
end, overlapping the previous wrap by a 1/2 width or so with each turn.
This would give you about twice the insulating value and no gaps in the
On Wed, 22 Jun 2005 13:13:55 -0500, HerHusband wrote:
I wish I could slope the duct down, but I have to route the duct about 2
feet over and 4 feet up to vent through an outside wall.
Thanks for the idea of using the fiberglass bats, that sounds like it would
work quite well. Not too hard on this short run either. I might do that if
I can't find 4" pipe insulation locally. So far I found only 6".
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