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I'm planning to install a roof vent for a bathroom exhaust fan I'm putting in. I'm thinking about using one of these:

roof cap

but I was wondering if I need to worry about it getting blocked by ice or snow? (I live in Minnesota.)

  • I guess my question is more about whether there's a different type of roof fixture I should use instead – Brad Mace Oct 17 '12 at 20:49
  • I also live in Minnesota, and have a bathroom vent that looks very similar to that one. It has never been blocked by snow since I've had the house. Remember your bathroom exhaust will be warm humid air; it will melt snow around it. Sadly, this snow will then turn into water, which will run down your roof, and then freeze again turning into ice, potentially causing ice dams if there's enough of it. But I've never had that much of a problem with mine. – meddlingwithfire Jan 12 '14 at 2:58
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Such a vent terminal can work, depending on your roof's micro climate. Depending on prevailing wind, solar orientation, drifting patterns, etc. there is often an area of the roof, usually near the ridge, which is relatively free of snow. If you must vent on the roof, this is where it should go, regardless of the type. As B. White indicated, a wall outlet is preferable, though even that can be partially blocked by rime ice.

Even when covered with snow, depending on the duct configuration in the attic (if there is one), enough heat can be emitted even when not in use to maintain a free air passage through the snow. When actually used, the heat serves to enlarge the path. However, it also causes an ice surface to form around the passage, limiting further expansion. In addition, the expelled moisture contributes more ice, such that the passage can get smaller, and possibly even blocked. Much moisture though, ends up collecting as rime ice, which can grow to block the passage as well. Fortunately, it is a fragile structure that collapses during any occasional thaw.

If not located in a relatively snow free region, the terminal can be sheared off by moving snow, or crushed. Even if the roof does not shed snow, if it is sloped, the snow pack will slowly creep, eventually crushing or breaking fragile roof appurtenances.

If your roof gets heavy snow pack everywhere, you can use stack terminals such as those used for gas vents. They can be extended up any distance to remain above the snow pack. They still need to be located near the ridge to avoid damage.

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I have one, I'm in MA, it causes the snow to melt around it, run down to colder areas and freeze, creating ice damns on either side of it. Never had an issue with it being blocked. I plan on changing it out this spring because of this issue, I extended it all the way down the roof two years ago hopping it would correct it, it didn't.

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It depends on where you live (sorry to state the blindingly obvious) but yes, any vent on a horizontal or semi-horizontal surface can get blocked by snowfall.

It would be better to vent out the side of the house where that is not an issue. It may even be "code" to do so.

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I live in Ontario and just coming out of a major deep freeze and found out the hard way that style of vent shown caused a massive ice dam all around the vent. The vent ended up buried in snow and started to drip into the bathroom. Cleaned off the snow and problem stopped for now, but plan to install a vent stack this spring.

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I have this style vent and ended up with water dripping into my bathroom through the pipe this winter. (northern Michigan) It has gone through multiple winters without any issues but this year is particularly bad with one very windy snowy day when the issue started. It did manage to clear itself and the vent is working again. I'm certainly going to get that vent replaced with something that has an extension pipe. Unfortunately it's not anywhere near the ridgeline either... more than halfway down the slope. I originally thought about using a soffit vent instead but the roofers that replaced my roof said that they've never had any complaints about this style.... they will have a complaint now.

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