# Bathroom fan ducting



## dale rex (Jun 10, 2012)

Is 16 feet too long of a run to vent through a gable? I can duct up through the roof, but i am concerned about snow laying on the roof and blocking the roof cap. Its a 4/12 roof.


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## griz (Nov 26, 2009)

Depends on the size of your fan & duct.

Might have to go with an inline.


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## dale rex (Jun 10, 2012)

The bathroom is small and only needs 50 cfm. I upsized the fan to 80 cfm to hopefully overcome the long run. If I go horizontal out the gable I plan to use rigid 4 inch pipe, and insulate it. It would be much easier to go up thtough the roof, would only be a 4 foot vertical pipe, but my main concern is snow buildup.


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## griz (Nov 26, 2009)

I built in snow country for a number of years.

Murphy crickets solved many problems like what you have.


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## nickko (Nov 11, 2012)

Go through the roof. I have been doing it for thirty years. Use a broan roof hood that is made for a bathroom fan. They usually sell them at the big box stores right next to the fans. The way they are designed the snow has no effect on them. Wrap some insulation around the vet pipe to stop the pipe from condensation. I always use four inch rigid pipe and foil tape all the joints.

good luck..........nicko


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## We Fix Houses (Aug 15, 2007)

Just had the same decision. Gable 2x the run. Through the roof with 2 exhaust into 6"x10" Broan type black roof vent from these folks.


http://www.luxurymetals.com/roofcaps.html#anchor_350


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## Mordekyle (May 20, 2014)

Can you Vent through Soffit or bird blocking? 


Sent from my iPhone using Tapatalk


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## MarkJames (Nov 25, 2012)

16 feet is nothing. Use hard duct.


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## SLSTech (Sep 13, 2008)

The question is how many bends or jogs do you have to do (one 90 is equivalent to 5') - 16' to 20' is my max recommendation before going to inline or going through the roof
http://thehtrc.com/2013/getting-details-right-bathroom-exhaust-venting


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## hdavis (Feb 14, 2012)

20'


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## Mr_Stop (Aug 15, 2016)

Mordekyle said:


> Can you Vent through Soffit or bird blocking?
> 
> 
> Sent from my iPhone using Tapatalk


Of all the options, soffit's are the one of the worse places to vent. The only thing worse would be running the duct into the eave. You run the risk of pulling the moisture back into the attic (assuming there are eave vents). I believe Panasonic just introduced a new soffit vent termination to help better address soffit venting.


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## mstrat (Jul 10, 2013)

Through the roof is almost always my choice...and rigid pipe. Flex duct seems like a problem waiting to happen...fills with condensation and water sits in it.


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## Tinstaafl (Jan 6, 2008)

mstrat said:


> Through the roof is almost always my choice...and rigid pipe.


Any roof penetration has potential for leaks. Gable for the win, as long as it's reachable without excessive ducting.

I'd do a roof vent vs soffit, though.


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## mstrat (Jul 10, 2013)

Tinstaafl said:


> Any roof penetration has potential for leaks. Gable for the win, as long as it's reachable without excessive ducting.
> 
> I'd do a roof vent vs soffit, though.


Agreed...if a gable is close enough that is the choice. Seems like a lot of hip roofs going up around here lately, with gables on the front...except the house we're building currently, 3 perfect gables to route it through with the vent flashed nicely.


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## Justin Roy (Jul 1, 2018)

Go ahead and hard pipe it. 

Justin
https://www.lafoundationrepairs.com


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## dale rex (Jun 10, 2012)

I ended up ducting through the gable with 4 inch PVC sewer and drain pipe(the smooth green stuff). Insulated with 5 inch insulated flex duct slipped over the PVC. The fan works fantastic, no noticeable loss in output from the 16 foot run. I did oversize the fan to help to overcome the long duct run. FYI, I used a Delta Breeze fan special ordered from Home Depot. Great fan, LED light and super quiet. Beats Broan and Nutone ( not quite as good as Panasonic) in my opinion, would definitely use another.


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## Big Johnson (Jun 2, 2017)

Tinstaafl said:


> Any roof penetration has potential for leaks. Gable for the win, as long as it's reachable without excessive ducting.
> 
> I'd do a roof vent vs soffit, though.


What’s wrong with through the soffit? That’s how my lazy ass HVAC guy always does it.


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## dale rex (Jun 10, 2012)

It was originally ducted through the vented soffit, and was not a good situation. The builder simply used flex duct and turned it facing downward to vent out through the little perforations in the vented vinyl soffit. After 20 years of the old fan operating like that the underside of the roof sheathing in that area was covered in black mold. I looked at it in the winter and the sheathing was also covered with ice on the underside. Thats why I hesitated to vent through the soffit again after seeing that mess.


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## Big Johnson (Jun 2, 2017)

dale rex said:


> It was originally ducted through the vented soffit, and was not a good situation. The builder simply used flex duct and turned it facing downward to vent out through the little perforations in the vented vinyl soffit. After 20 years of the old fan operating like that the underside of the roof sheathing in that area was covered in black mold. I looked at it in the winter and the sheathing was also covered with ice on the underside. Thats why I hesitated to vent through the soffit again after seeing that mess.



I always use solid soffit 4’ each side of where the soffit vent is located. 

There’s a code but I can’t remember exactly what it is.


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## Tinstaafl (Jan 6, 2008)

Big Johnson said:


> What’s wrong with through the soffit? That’s how my lazy ass HVAC guy always does it.


As Dale mentioned, that moisture-laden air tends to get sucked right back up into the attic space. You may just have a winning formula with your 4' of unvented soffit, but I'd class you as an albino rhinoceros for doing that.

Most guys just plow ahead with the vented and call it good.


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## Big Johnson (Jun 2, 2017)

Tinstaafl said:


> As Dale mentioned, that moisture-laden air tends to get sucked right back up into the attic space. You may just have a winning formula with your 4' of unvented soffit, but I'd class you as an albino rhinoceros for doing that.
> 
> Most guys just plow ahead with the vented and call it good.


I was working on a house years ago and we used to have this really cool HVAC inspector (he retired) he saw the vents were hanging down out of the eaves and mentioned the code to me, so I’ve been doing that ever since. I’ve had to go back a couple times and swap out lanced for solid when vents were added latter. You really don’t miss 10’ feet or so vented soffit as the vented soffit provides way more venting area than the ridge vent on your average house. I do use a gable if ones practical as I’m running the ****ter vents, I seem to do a lot of hip roofs though.


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## SLSTech (Sep 13, 2008)

Big Johnson said:


> I always use solid soffit 4’ each side of where the soffit vent is located.
> 
> There’s a code but I can’t remember exactly what it is.


M1506.3 Exhaust Openings: Air exhaust openings shall terminate not less than 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable and nonoperable openings into the building...


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