Frozen bathroom exhaust piping


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Old 01-24-13, 11:12 AM
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Frozen bathroom exhaust piping

With the cold weather (-35'C to -45'C) this past week, I noticed the flex tubing (dryer vent stuff) for the exhaust fans in two of our bathrooms is frozen solid in the attic. One of the exhaust tubes is insulated wrapped, and one isn't (both frozen).

From what I am seeing, the moisture in the air is turing into water as soon as it hits to attic tubing and collecting in the low spots to freeze.
I'm planning to switch the tubing out for insulated stuff, but this won't help keep the moist air from turning to water once it hits the cold air in the attic.

Any suggestions?
 
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Old 01-24-13, 11:27 AM
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This is interesting as I also have two bathroom exhausts exiting through my cold attic to gable vents of which I am concerned. I am not sure how the vent would be completely blocked unless it was entirely filled with water which would be either a very significant low spot in the line with alot of water in it (could be helped by using solid vent pipe - not flex) or you are not running the fan long enough to be pushing dryer (more dry - not the clothes dryer) air to purge the vent line. For the low spot issue, could you raise the exhaust line closer to the fan so that it would drain out the exterior end of the line instead of sitting?

I also read a forum post some time ago about the outside vent icing over and not allowing the air to exit. Not sure how that was resolved.
 
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Old 01-24-13, 11:39 AM
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pjaffe,
There was a bit of a sag in the tubing which probably got worse as water accumilated. The pipe work isn't ideal currently as it rises up ~5' from the attic floor to the dormer wall which it exits via a dryer vent exit (no dryer involved).

Under normal (90% of the time), the fan is able to move the moist air up and out. For about a week a year, we have -30'C weather or colder. This week is that week.

What I am thinking of doing is replace the existing tubes with insulated flex or fixed tubing. Have it come straight up from the bathroom ceilings onto the attic floor. From the attic floor, 90 degree and flat run along the floor to the gable vents.
This should reduce the exposure a bit to the cold, while maintaining a relitively flat run and down. The only place the moist air could condense is at the 90 degree bend.
 
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Old 01-24-13, 12:30 PM
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Best is to use rigid metal duct throgh the roof.
 
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Old 01-25-13, 05:56 AM
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Originally Posted by ray2047
Best is to use rigid metal duct throgh the roof.
You are thinking straight up and out the roof top?
My attic is 12ft in the center, and at least 5ft high where the bathroom vents come through the floor boards in the attic. That would be a lot of cold metal.
 
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Old 01-25-13, 06:28 AM
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But no place for water to collect and freeze or am I misunderstanding.
 
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Old 01-25-13, 07:39 AM
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Originally Posted by ray2047
But no place for water to collect and freeze or am I misunderstanding.
True. Will make sure the fans are of enough CFM to cover the straight up run (which they should be).

I had replied to this post already, but must have not waited the 180 seconds and then closed the tab.
 
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Old 01-25-13, 12:30 PM
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If you do decide to go horizontal, include a bit of a drop (1/4" per foot or so) toward the outside, so the water has somewhere to drain. I would also recommend the use of rigid metal ducting and then insulating with the silver-faced duct insulation. The rigid duct will also help with the airflow.
 
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Old 01-25-13, 12:36 PM
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Originally Posted by Zorfdt
If you do decide to go horizontal, include a bit of a drop (1/4" per foot or so) toward the outside, so the water has somewhere to drain. I would also recommend the use of rigid metal ducting and then insulating with the silver-faced duct insulation. The rigid duct will also help with the airflow.
I'm assuming the bigest issue with the current arrangement is the ribs of the flex tube distrurbs the air flow enough to seporate the moisture from the air. Also contains more surface area for the moist air to contact and cool to seporation.

The more I think about this one off issue, the more I think the fans have enough force (CFM). This was a non-issue last winter. That being said, we didn't have a week of -35'C to -45'C weather. We may have hit -30'C once or twice last winter.
 
 

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