Venting bathroom fan to ridge vent - is it ok?

I live in a one story house with an unfinished attic. Currently, the bathroom fan is vented by a 3" PVC duct that passes through the attic and out the roof. The attic gets cold (blown in rock-wool insulation lays between the foor joists) and the humid air being vented from the bathroom condenses. Unfortunately, the PVC is sloped the wrong way so condensate is dripping back through the fan and into the bathroom. Messy, and damage to the bathroom ceiling is occurring.
I'm planning to replace the fan with a quieter one with more volume, and I'd really like to avoid having to put another hole in the roof, and I also don't want to use the present ducting.
A builder who helped with some other renovations has told me that it's ok to run the fan exhaust duct (it'll be 4" diam) up to just beneath the ridge vent, and to allow the exhaust to vent through the ridge vent. Is this likely to work, and is it an acceptable way of venting? I wonder about blowback and about iceing during the winter.
Also, is it reasonable to insulate the exhaust ducting to minimize condensation within it?
Thanks for any comments or suggestions.
Bill Christens-Barry
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Wm A Christens-Barry, PhD
Equipoise Imaging, LLC
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This is a question for you local building authority. Personally I would consider using the old pvc and insulate it. I would not want a fart fan venting into the attic, cause around here that is not acceptable. Hence the roof penetrations.
Your going to have some problems with the 3 inch pipe. Everything I have seen recently is 4 inch or larger.
alternate solution vent to the eves.
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Bill Christens-Barry wrote:

It get's done that way, but it is a very poor idea.
I am guessing you are talking about eave vent which is what many do. Most of the warm moist air just ends up in the attic causing trouble.
If it is the ridge (top of the roof) that may be better, but again there will be more warm most air in your attic that should be there. Do it right and put it through the roof.
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Joseph Meehan

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If you get condensation in the exhaust duct now, I expect you'll get condensation in your attic if you vent it within the attic, even at the ridge vent. That's bad -- not just ice in winter, but water that promotes rot and mold.
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snipped-for-privacy@phred.org is Joshua Putnam
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Vent it to the eve's, where there is a vent,If you go to the ridge(peak) won't the condensation still run down the tube into the bathroom, had mine that way (eve) for 11 yrs, just replaced the fan in the bath this weekend, covered the 4" tube with extra insulation. I installed a 130cfm, Nataluis $99.
Tom

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twfsa wrote:

And some will go out the vent and some will go into the attic and make trouble. Even some that does go out will come right back in. The normal air flow is IN the eaves and OUT the high vents.

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Joseph Meehan

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Joseph is right, some of the moisture from the bath fan can get sucked back into the attic through the eave vents.

I can highly recommend Panasonic fans. They use squirrel cage fans and are VERY quiet. We have three in our house and are quite happy with them.

I tried to minimize roof penetrations in our house too. We only have two, a large plumbing vent pipe and the woodstove chimney.
Our bath fans get ducted through the attic and exit out through gable end walls. It's a slightly longer run, but they do not penetrate the roof and the exhausted moisture isn't anywhere near an eave vent to get sucked back into the house.

Yes, and slope the ducting towards the exterior vent so any condensation can drain away. Best to use rigid ducting like PVC rather than those flexible corrogated things.
In our case, the ducting runs through a heated area, but I would insulate the ducts otherwise.
Anthony
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Just inslate the existing pvc pipe in the attic
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