Bathroom fan with inaccessible attic

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KevP
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Bathroom fan with inaccessible attic

Post by KevP » Sun Mar 17, 2019 9:12 am

Hey guys,
A portion of my second floor rooms have inaccessible attic above it (above rooms and bathroom). My second floor bathroom has no fan and this has been an issue with moisture making all walls and windows moist. We are in Minnesota so opening windows in winter is really not that an option . I am planning on opening two spots, one for the fan housing and one to connect the duct to the vent. Only issue is that the joists run parallel to the gabble wall. I can go out of the roof but with the amount of snow we get here i feel like that is not a good option. Im planning on getting a Panasonic fan but i see that their manual states running 2 to 3 ft of straight run before any bends. I might have at most 1 to 2 ft before taking a turn. I know using the flex is much easier that the rigid but i need to have the duct over the joist to the side. Does this sound like a good way to go for it? I will use an 6 inch R8 heavy duty jacketed since this is going to be in unheated space. I think this will be at most 3 to 5 ft of ducting.
Also does it make sense to open up the the ceiling in the bathroom or should i do it in the adjacent bedroom so i can leave an access panel? Is that necessary? I will upload a picture of the outside as well. It shows the bathroom and bedroom windows plus the location of the vent im thinking
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The wall on the other side which is the bedroom
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Shannon
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Re: Bathroom fan with inaccessible attic

Post by Shannon » Sun Mar 17, 2019 1:40 pm

So the main problem with a bend so close is you get more noise then what you normally would and sometimes you can’t avoid that. Go as far from fan and as gradual bend as you can to make the turn. I would just use flex for the short distance you are going.
Also I would just use the bathroom ceiling there is really no need to access after. Get it all installed and try it for a bit before finishing the patchwork on ceiling.
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KevP
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Re: Bathroom fan with inaccessible attic

Post by KevP » Sun Mar 17, 2019 2:08 pm

Thanks Shannon. I read somewhere that aside from the noise, an immediate bend can cause the air to comeback in like an obstruction. But is taking a turn and going over the joist ok? I guess thats my only option

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Shannon
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Re: Bathroom fan with inaccessible attic

Post by Shannon » Sun Mar 17, 2019 3:54 pm

Yes that is why causes the extra noise.
A turn and over the joist to close to the fan will cause the same issues. It still ventilates but you get some air turbulants that make extra noise.
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A. Spruce
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Re: Bathroom fan with inaccessible attic

Post by A. Spruce » Sun Mar 17, 2019 4:16 pm

I agree with Shannon on all points.

Because it's such a short run, flex will be fine. When you install it, put a gentle curve in it, there's no reason to make hard corners unless there are obstructions nearby that require it. Make sure that your outside vent cover has a damper in it so that you don't get cold air blowing back into the bathroom.
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KevP
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Re: Bathroom fan with inaccessible attic

Post by KevP » Sun Mar 17, 2019 5:06 pm

Thanks for all thr input. Im definitely getting an exterior vent with a damper. I believe the Panasonic fans also comes with a built in damper.

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Shannon
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Re: Bathroom fan with inaccessible attic

Post by Shannon » Sun Mar 17, 2019 6:50 pm

Ya most all fan units come with a damper but for sure use one on the exterior as well.
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