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Discussion Starter #1
I currently have only windows in the bathroom and want to install an exhaust fan with roof vent. I can get into the attic area above bathroom, but really have to slither, there isn't much room to move.

I have a gable vent that is 5 ft away from where the bath fan will be.

Questions.
1. From my readings, it seems I should put the roof vent away from the gable, at least 10 ft or does that not matter?

2. Is going straight up from the bathroom vent a good idea? I Would only need 3 ft of flex or solid venting pipe. Or is there a certain distance away from the bathroom I need to go to lessen noise?? I think I read 10 ft? Common sense to me says get a shorter run, less resistance, less heat loss.

3. I live in the northeast and I am concerned with snow covering the vent, is there another kind of vent or do I not have to worry.

4. Rather than using flexible ducting, should I use metal? Can PVC be used? If I understood correctly you can't use pvv due to "IMC section 603.8.3 Plastic ducts and fittings. They are allowed for underground duct only."

I then read that a master plumber say he uses schedule 40 PVC pipe and send the exhaust up through the roof. Once the pipe exits the roof, use a gentle sweep 90-degree angle followed by a 45-degree bend to prevent rain water from entering the exhaust pipe. Be sure the end of the pipe is at least 20 inches above the roof so it's never blocked by deep snow.
The. He says he uses 3 inch foam insulation".

I would appreciate any insight. Thank you!
 

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retired framer
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I would go out the gable with an insulated flex duct. set the flex on a piece of plywood or board and prop one end so it runs down hill to the outside vent so any condensation drains outside.

How far from the gable vent can you put it? Should be 10 ft.
 

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Discussion Starter #3
If I put it through the gable vent, then wouldn't I be effectively sealing that as an airway? I wouldn't be able to allow venting of hot air and allow air to blow that back in. Did I misunderstand?
 

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retired framer
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If I put it through the gable vent, then wouldn't I be effectively sealing that as an airway? I wouldn't be able to allow venting of hot air and allow air to blow that back in. Did I misunderstand?
I'm lost.:wink2: You have a vent in the gable?
It is the high vent with other low vents
or is it a low vent with other high vents.

Can you go out the gable and stay 10 ft from that other gable vent?
 

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Discussion Starter #5
I have 3 gabled dormers with 3 gable vents. I do not have any ridge vents or soffits, it is a 1929 house. The attic in the bathroom is at most 3 ft tall and maybe 4 ft wide.
The light fixture, that will be replaced by an exhaust light combo is maybe 5 ft from the gable vent in the gabled dormer. Hope that makes sense.
 

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In the frozen tundra of NY we put them through the roof frequently. Use a roof exhaust vent hood that is made for the purpose. Rigid duct is better than flexible and insulate the duct if you can. Use a short run supported so there are no sags and keep it away from other vent openings so it can’t short circuit and go back in through another vent. Snow won’t bother it, snow can absorb plenty of warm air until it melts back away from the vent.
Sometimes I use 4” rigid aluminum duct inside a 5” insulated flex duct.
 

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Discussion Starter #11
Thanks for your help. I contacted panasonic, but they weren't too helpful. I took some measurement and the bath fan will be 5 ft from the gable vent. It seems like I can only go another 5 ft away from the exhaust fan (10 ft away from the gable vent) Iand then I would have to go vertical just because of how the roof is. Would that be fine?

I was told by panasonic not to do a 90 degree bend even after going 2 to 3 feet. They said do 2 45 bends. So my thoughts are run a 3 ft horizontal, 45 angle, 2 ft, 45 angle. I figure I should run the piping before the roofer comes so then they can then they can connect the pvc? It seems like the electrician and roofer are thinking of using flexible pipe. What grade/ schedule pvc do I use?

I am surely overthinking this entire thing, but do I need any slope for the pipe? My concern is that if water vapor does not go out, it will come back to the fan and you get water stains. Perhaps this only happens when you don't insulate the pipe or if you use flex pipe and some of the condensation gets caught in the ridges?
 

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How far is the closest eave?


You can use a fixed 90, go directly horizontal to another fixed 90 and use an eave vent.


Or just run it all in insulated flex.
 

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Discussion Starter #13
I can't get to an eave because they built knee walls and my rafters are 4.5 inches. So it has to come out of the roof.
 
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