# Bathroom exhaust fan. Is it ok to vent it through attic & up to ridge vent?



## lola123go (May 7, 2010)

I'm not sure what to do...so many opinions! 

Do you think I will have problems with condensation dripping down through the bathroom exhaust fan or moisture in the attic?

If I ran a duct from the bathroom ceiling over to the roofs ridge vent, it would travel approx 12 feet. Is this too far? 

Thanks! 

(I live in Baltimore MD)


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## Nestor_Kelebay (May 7, 2010)

Lola:

     No, that's not too far.  The bathroom ceiling fans in my basement suites have 20 feet of vertical duct to go through before coming out the vent caps on my flat roof.  But, if I were you, I would go the shortest straightest route to get out your roof.

The bottom line is that the shorter, straighter and smoother your bathroom fan vent ducting is, the easier air will flow through the duct and so the higher the volume flow rate through the duct, and the better the fan will work.  The following web site shows the "length equivalents" for common fittings for water flow through various sizes of water pipe.

http://www.engineeringtoolbox.com/resistance-equivalent-length-d_192.html

      You can see that any perturbation on the ID of the pipe (such as would be caused by a valve or a tee) or change in direction of the flow (as would be caused by a 45 or 90 degree elbow) offers resistance to flow which is expressed as an equivalent length of pipe.  There are similar charts for air flow through various size ducts.  The length of your duct and any bends in it, and even the roof vent on the end of the duct are all going to increase the resistance to air flow, and reduce the air flow rate out of the bathroom when the fan is on.

     Since many of the most common problems associated with bathrooms arise from poor or non-existant ventilation, ensuring you have good ventilation in a bathroom is a wise investment, and you don't want to cut corners here.

     So, if it were me, I would use an insulated duct (or insulated it yourself) and have your bathroom fan duct go straight up from the fan through your roof.  Any shingle roofing company would be able to install a fan vent on your roof, and this is the kind of thing that you typically only do once in a blue moon, or whenever you add a bathroom to your house, so it's not like it represents a major expense when you consider it's something that's done seldom and greatly affects the comfort of your house.  (In some houses even here in Winnipeg, there are windows instead of ceiling fans (the building code here required one or the other at one time), and the condensation problems some people have on those windows in winter is Gawd-awful.  A good bathroom ceiling fan that works well will make your house more comfortable to live in by reducing condensation and mildew problems and eliminating excess humidity from your environment.)

     I have also heard of people running the fan duct out a soffit along the side of their house.  The problem that may occur there, however, is that an condensation that does form inside the duct will leak out at the duct joints and possibly cause water damage to the ceiling in places inside your house.


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## oldognewtrick (May 7, 2010)

You are better off running the shortest route to a dedicated roof exhaust vent. They make vents that have flaps that close when not in use and prevent back drafts into the vent pipe. I believe that venting to a ridge or to a sofit is against most local building codes.


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## abrowning (May 10, 2010)

I echo the previous answers of taking the shortest route to a dedicated roof vent.

And I'm curious about how you would connect to the ridge vent. Is there a special fitting for that? If not, you would be asking for a mold problem. My neighbor let his bathroom exhaust fan duct in to the attic for just a few weeks (not sure why) thinking that the open attic windows would allow the moisture to escape. He ended up with a BAD mold problem up there.


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## oldognewtrick (May 11, 2010)

The problem is the ability of the fan to push heavy moist air in a verticle flow. I know of no attachments for ducting to a ridge vent, doesn't mean there isn't one made tho.


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## handyguys (May 11, 2010)

code in my area allows the bath vent to be directed into a soffit vent. That's the easiest and cheapest thing to do for the builder and how mine was done. I intend to do a proper vent out the gable end someday.


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## oldognewtrick (May 11, 2010)

handyguys said:


> code in my area allows the bath vent to be directed into a soffit vent. That's the easiest and cheapest thing to do for the builder and how mine was done. I intend to do a proper vent out the gable end someday.



Handyguy, if you get one of the roof vents with a flap, keep the run short, it will work better than running to the gable vent. The vent with the internal flap helps reduce back drafting of cold air. They are fairly cheap ($20 or so) and pretty easy to install.


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## handyguys (May 11, 2010)

hey, thanks for the advice oldog/newtrick. I should have been more precise. I want to put an exhaust vent into the gable end wall which is near the bathroom. I prefer to go that route, versus having a roof penetration.


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## Wuzzat? (May 11, 2010)

Nestor_Kelebay said:


> Resistance and Equivalent Length of Fittings


I think this link is for water flow, not air flow.


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## kingz1032 (May 13, 2010)

This is where I got my  bathroom fan. It works really well in terms of exhaust, and they help you set up and answer any questions. It also looked very nice in my bathroom.


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## lola123go (May 14, 2015)

Thanks so much for all of your replies! (... 5 years later, better late than never)


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## zannej (May 15, 2015)

Did you ever get the bathroom fan installed?


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## Sparky617 (May 15, 2015)

I was wondering why a 5 year old post bubbled up to the top until I got to the second page.

I remember Nestor from Handymanwire and HGTV's now retired boards.  Looks like he fell off the face of the earth everywhere.  Anyone know what happened to him?   He was always good for very detailed answers especially on paints and coatings. 

Back to the original question, in one of my townhouses the national builder stopped the vents just below the ridge vent.   I understand now, 25 years later that this is not a good idea and they should go through the roof.  Running them to the soffit vents allows the air flow to bring the moist air back into the attic space.  If you have a gable end you can run them through there as long as there is good separation from the soffit or gable vents.

My current house runs them thru the roof, though for both upstairs bathrooms it wouldn't have been any further to run them out the gables and saved a roof penetration.


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## oldognewtrick (May 15, 2015)

Nestor self imposed his own exile after disagreements with other members here. And yes, he has a vast knowledge of paints and coatings.


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## Sparky617 (May 16, 2015)

oldognewtrick said:


> Nestor self imposed his own exile after disagreements with other members here. And yes, he has a vast knowledge of paints and coatings.



He dropped off the other sites as well.  He could be entertaining.


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## Joel (May 21, 2015)

handyguys said:


> hey, thanks for the advice oldog/newtrick. I should have been more precise. I want to put an exhaust vent into the gable end wall which is near the bathroom. I prefer to go that route, versus having a roof penetration.



From what I understand, this is the preferred route in cold climates where warm air exiting the roof could melt the snow and create ice dams.


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