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Old 05-10-2010, 02:36 PM   #1
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Bathroom Fan Venting


I have a fan / light combo in my bathroom that as I discovered this weekend isn't vented properly, in addition to being buried under sheets of insulation (yellow bats, fairly rigid - no clue what they actually are.) There is a flexible metal duct running from the light but it doesn,t go anywhere. To vent this, does it have to vent up through the roof or can it be directed to the large attic vent that is a few feet away?

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Old 05-10-2010, 04:11 PM   #2
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Bathroom Fan Venting


Modern building codes require bathroom vent fans to vent directly outside, not into the attic. So either you would need to either go through the roof, through a wall, or through the roof soffit.

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Old 05-10-2010, 04:45 PM   #3
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Bathroom Fan Venting


That's what I thought. Would mounting a bracket to the existing vent (fixed louver - 24x36) not suffice or does it need its own exit?
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Old 05-10-2010, 06:18 PM   #4
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Bathroom Fan Venting


Doing what your asking is better than what you have now but it should have it’s own exit point out the wall (#1) or the roof.
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Old 05-11-2010, 01:05 AM   #5
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Bathroom Fan Venting


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Originally Posted by cellophane View Post
Would mounting a bracket to the existing vent (fixed louver - 24x36) not suffice or does it need its own exit?
I think the purpose for the code is to insure the moist air from a bathroom doesn't collect inside the attic, therefore you would have to have this bracket holding the exhaust pipe flush to the louvers to make sure all the moist air gets forced out of the attic... but the louvers themselves will effectively cut the cross sectional area of the exhaust... so what you would really need is something like a 4" to 6" transition piece, mount the 6" piece flush against the louvers and the bathroom exhaust to the other side. But of course doing this than reduces the cross sectional area of the louvers to ventelate the attic.

So perhaps the best all around would be if you used the openning of the louvers as the wall penetration for the bathroom... basically pretend that the louvers are a wall that you would cut through and mount what ever terminator to the louvers that you would mount if you went through a wall. That way, you only take up about a 4x4 area of the louvers. Of course if these louvers face the road... it might look a little akward (but maybe not if its all solid white in color).
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Old 05-11-2010, 08:54 PM   #6
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Bathroom Fan Venting


IF you mount the fan exhaust in the louvers, seal the rest of that louver closed. The air exhausting would possibly return back into the attic if your attic ventilation system is not balanced. If a gable exhaust vent louver, page 606: http://books.google.com/books?id=Z8a...0vents&f=false

http://www.rd.com/how-to-install-a-q...icle18312.html

http://www.efi.org/factoids/bathroom_sizing.html

Be safe, Gary
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Old 05-11-2010, 09:40 PM   #7
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Bathroom Fan Venting


Quote:
Originally Posted by HooKooDooKu View Post
I think the purpose for the code is to insure the moist air from a bathroom doesn't collect inside the attic, therefore you would have to have this bracket holding the exhaust pipe flush to the louvers to make sure all the moist air gets forced out of the attic... but the louvers themselves will effectively cut the cross sectional area of the exhaust... so what you would really need is something like a 4" to 6" transition piece, mount the 6" piece flush against the louvers and the bathroom exhaust to the other side. But of course doing this than reduces the cross sectional area of the louvers to ventelate the attic.

So perhaps the best all around would be if you used the openning of the louvers as the wall penetration for the bathroom... basically pretend that the louvers are a wall that you would cut through and mount what ever terminator to the louvers that you would mount if you went through a wall. That way, you only take up about a 4x4 area of the louvers. Of course if these louvers face the road... it might look a little akward (but maybe not if its all solid white in color).
IMHO using an adapter from the exhaust vent to the louvers (Louvres, in Canada) would not help. Because the louvers are designed for a strong fan that covers the entire cross section of the opening and are raised and lowered through the fan activation. In this case, the output of the exhaust fan will not be strong enough to raise them to vent properly. Therefore, a separate opening through the wall or roof will be required.!

Last edited by spark plug; 05-11-2010 at 09:41 PM. Reason: Missing letter (S).
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Old 05-11-2010, 10:30 PM   #8
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Bathroom Fan Venting


For bathroom exhaust, you can just run the flex duct to a soffit vent.
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Old 05-12-2010, 07:38 AM   #9
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Bathroom Fan Venting


Running to a soffit vent can allow the moisture to re-enter

When you say louver vent - do you mean a gable vent on one end ?
IE - the louvers are always open ?
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Old 05-12-2010, 08:44 AM   #10
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Bathroom Fan Venting


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Originally Posted by Scuba_Dave View Post
Running to a soffit vent can allow the moisture to re-enter

When you say louver vent - do you mean a gable vent on one end ?
IE - the louvers are always open ?
correct. it is a gable vent. my appologies on the terminology mish-mash.
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Old 05-12-2010, 12:05 PM   #11
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Bathroom Fan Venting


This Old House just about 2 weeks ago did a thing where the exhaust went to the soffit and they showed that the moisture coming back into the attic was causing mold around that area. This one really shocked me because in my area almost all new construction and additions vent to the soffit and they use those white mesh concave plastic things at the exit point. You can literally count bathrooms in a house by how many of those things are under the soffits.

I agree that blowing back into the house is bad, but if you live in a snow area can't the vent through the roof get blocked? on This Old House the vent cap they used was only liked 4 or 5 inches high?
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Old 05-12-2010, 01:49 PM   #12
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Bathroom Fan Venting


Aren't we talking about a fart fan here? Usually mounted in the center of a bathroom on the ceiling. Also used to exhaust the moisture after a hot shower.

I could understand a dryer vent or a kitchen downdraft, but a bathroom exhaust is rarely run long enough to produce condensation on the inside of your soffit. Hardi soffit won't mold anyways. I could maybe see mold forming in colder climates, but in the south, the warm shower air is usually less humid than the outside summer air.
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Old 05-12-2010, 07:55 PM   #13
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Bathroom Fan Venting


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Originally Posted by Houston_Bldr View Post
Aren't we talking about a fart fan here? Usually mounted in the center of a bathroom on the ceiling. Also used to exhaust the moisture after a hot shower.

I could understand a dryer vent or a kitchen downdraft, but a bathroom exhaust is rarely run long enough to produce condensation on the inside of your soffit. Hardi soffit won't mold anyways. I could maybe see mold forming in colder climates, but in the south, the warm shower air is usually less humid than the outside summer air.
Whether it is done or not (venting to the soffit) it is wrong. Because the humid, unexchanged air is causing for mold spores to grow.!
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Old 05-18-2010, 03:07 PM   #14
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Bathroom Fan Venting


Assuming you can access the roof safely, venting it through the roof is really not a difficult project. I was a complete DIY moron but I did it myself after finding an instructional video on-line. Hasn't leaked yet, a year later.

As for snow blocking a roof vent, we got a ton of snow this past winter without any problem. I found the warm exhausted bathroom air did a good job of melting the snow in front of the vent and keeping it clear. I suppose if your roof was flatter or the snow super deep it might be a problem.
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Old 05-18-2010, 03:30 PM   #15
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Bathroom Fan Venting


Venting exhaust fan into attic is a very big no no and a very large concern. The moisture will build up and cause severe damage if you do not remedy the situation. The vent should be connected via metal piping through the roof. The pipe MUST be insulated or again you will begin to build up moisture in the attic. DO NOT VENT IT THROUGH THE FASCIA! Many contractors and do it yourselfers will vent through the fascia the expelled moisture rises right back through the vent into the attic. This can lead to large remediation costs and pose a health concern due to the possible mold buildup.

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