# Bathroom exhaust venting



## oldsparky52 (Feb 25, 2020)

I have never gotten around to replacing the non vented bathroom fans that were originally installed in my home. I was talking to a friend of mine discussing how I would do it (after I lost some weight) and how much I hated the idea and process of doing it. 

Anyway, the discussion of venting came up and he was of the opinion that pointing the vent duct to the ridge vent would be fine. I know that's what a lot of people did in the early 70's, but ... IDK. My buddy (who is pretty sharp) said there would not be enough moisture to be a problem. I'm a little dubious about this since this practice was banned (where I worked) in the mid 70's. 

I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


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## Forge Boyz (Nov 7, 2014)

IF you were to do it, and I do think it is best to vent to the outside, I would end the vent in open space in the attic. Pick a place that has good ventilation, but make sure that the air will not be directed against any wood. If it is, over time the moisture will rot out the trusses or roof sheeting.
That being said, how hard would it be to run vent hose over to a gable wall? That is the easiest way to put in a vent. Drill a 4 1/2" hole in the wall and put in a vent cap.

Sent from my SM-G970U using Tapatalk


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## oldblue (Mar 2, 2013)

Adding the moisture to the attic isn't a good idea period, they're not hard to vent properly with a roof vent kit and even easier if you can hit a gable. My parents house had them dropped at the soffits, when it gets really cold the moisture freezes in the attic and leaves wet spots on the ceilings when it thaws. Why they choose the soffits over the high vents I have no idea but I see it done that way around here alot. Don't use the cheap flex at the box stores, grab some 4" flex the kind used for a heating supply vent with the insulation. The moisture can condense and build up in an uninsulated vent.


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## oldsparky52 (Feb 25, 2020)

oldblue said:


> Adding the moisture to the attic isn't a good idea period, they're not hard to vent properly with a roof vent kit and even easier if you can hit a gable. My parents house had them dropped at the soffits, when it gets really cold the moisture freezes in the attic and leaves wet spots on the ceilings when it thaws. Why they choose the soffits over the high vents I have no idea but I see it done that way around here alot. Don't use the cheap flex at the box stores, grab some 4" flex the kind used for a heating supply vent with the insulation. The moisture can condense and build up in an uninsulated vent.


How far is too far to hit the gable (thanks for that, I like that idea). It's probably about 20' to the gable. I guess I could get a high cfm fan and upsize the duct to reduce drag. Any suggestions on this?


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## 99cents (Aug 20, 2012)

All I know is that here it has to be insulated.


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## oldblue (Mar 2, 2013)

oldsparky52 said:


> How far is too far to hit the gable (thanks for that, I like that idea). It's probably about 20' to the gable. I guess I could get a high cfm fan and upsize the duct to reduce drag. Any suggestions on this?


Shouldn't be a problem. Different fans will recommend different lengths, which is based on equivalent length. Say 35' total but each 90 will count as 5' of pipe.


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## wcord (Jan 23, 2011)

Either vent out a gable or thru a roof jack. You don't want to vent any moisture into the eaves or attic
Absolutely critical is making a 'p' trap in the pipe. Cold air likes to flow back into the fan, and those built in backdraft dampers in the fan and exhaust hoods are a pos.
I usually use 5" or 6" insulated flexible duct and metal duct tape to seal the connections.
And dont buy a cheap 4" fan. They only make noise, don't move air


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## TGGT (Oct 28, 2012)

I vented my Panasonic light/heater/fan years ago. It really wasn't very hard. I'm no roofer, just watched a few videos and tarred the hell out of it. I used hard piping, so it is a little loud, I'm sure the flow is better, but might've gone with the flex duct next time. I didn't know anything about P traps, but we're in Texas so heat is more a concern than cold.


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## mofos be cray (Nov 14, 2016)

wcord said:


> Either vent out a gable or thru a roof jack. You don't want to vent any moisture into the eaves or attic
> Absolutely critical is making a 'p' trap in the pipe. Cold air likes to flow back into the fan, and those built in backdraft dampers in the fan and exhaust hoods are a pos.
> I usually use 5" or 6" insulated flexible duct and metal duct tape to seal the connections.
> And dont buy a cheap 4" fan. They only make noise, don't move air


I strongly oppose the p trap suggestion. Putting that number of bends in the pipe severely restricts the ability of the fan to ventilate the space. Further it provides a perfect location for moisture to condense out and accumulate. 
Allowing cool air into the building is imo far better than having a fan that does not work as intended.
Also, count me among the group that is against venting into the attic. That air has to exit the building.


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## joe-nwt (Mar 28, 2019)

I feel like an idiot but, what does a "non-vented bathroom fan" do?


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## MotoGP1199 (Aug 11, 2014)

joe-nwt said:


> I feel like an idiot but, what does a "non-vented bathroom fan" do?


I think they are mostly for filtering out the smell of a nice big dump, but thats about it. I can't imagine the charcoal filters work well for removing humidity on long steamy showers.


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## oldsparky52 (Feb 25, 2020)

joe-nwt said:


> I feel like an idiot but, what does a "non-vented bathroom fan" do?


LOL, I agree with that question. We never turn them on. I should have done this years ago, we basically don't have bath fans.


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## jw0445 (Oct 9, 2009)

I've torn some out that were non vented with no where for the air to go. Pretty much just covered the noises within. It was really loud.


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## Bourbon County (Aug 19, 2020)

I too agree with venting through the roof or gable wall if it's close enough. You live in a humid area and you don't want to add any additional moisture in the attic.

Absolutely do NOT route the ducting so it makes a trap, it will only allow a place for condensate to collect. If you use flex duct the weight of the water will eventually build up enough to pull the flex loose and restrict the airflow until that point. Keep the duct as short and straight as possible, make sure and make the connections as air tight as possible.

Another recommendation is buying an aluminum roof cap, they hold up much better than painted steel or plastic. Roof surfaces can get very hot and aluminum works best. I had my roof replaced a couple of years ago and just had them reinstall the 20 year old caps, they were as good as new.

Panasonic makes probably the best bath fans on the market now. Many models have ECM motors. They also make a wall control that will allow you to set a dew point to turn the fan on automatically if someone forgets to turn it on while showering and it can be set up to over run for up to 20 minutes to completely exhaust the humidity created from showering .This is a very nice feature during hot weather.


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## joe-nwt (Mar 28, 2019)

MotoGP1199 said:


> I think they are mostly for filtering out the smell of a nice big dump, but thats about it. I can't imagine the charcoal filters work well for removing humidity on long steamy showers.


Oh. So they are a charcoal filter fan for a bathroom? I had no idea.

I must lead a sheltered life.....


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## CMP (Oct 30, 2019)

oldsparky52 said:


> How far is too far to hit the gable (thanks for that, I like that idea). It's probably about 20' to the gable. I guess I could get a high cfm fan and upsize the duct to reduce drag. Any suggestions on this?


My favorite fan today is an inline fan with sheet-metal round ducting. If you have the room in the attic to mount the fan in the rafters.
About 18 years ago I used one of these in a handicapped bathroom remodel at the shop. Bought a 6" fan kit with two plastic inlet grilles and the fan, obtained a wall outlet vent with a back-draft damper built in. 

Put two inlet grilles in, one in the lavatory and one in the shower soffit, tied them together with a wye fitting. It pulls 100% of the vapors out of the shower no matter how long your in, and makes quick work of the commode smells. Most of the noise is where the fan is mounted, barley noticeable in the restroom. Many years of service and it works great, with a ball bearing motor and a plastic housing. Duct can be insulated with standard HVAC duct insulation, or fiberglass wrap.

Works way better than the last fan I used, a large CFM Nutone with a dual squirrel cage blower and a 4" x 10" sheet metal duct, straight up through the roof.



Fantech FR100 $133.25 Inline Centrifugal Duct Fan, 4 In. Dia. | Zoro.com

FR 100 Centrif. Inline Fan - Inline duct fans - Fantech

Accessories for inline duct fans - Fantech


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## WannabeTesla (Feb 24, 2020)

I'm with CMP on this- unless the intention is to cover up other noises. I wouldn't vent to a closed attic. I've never heard the p-trap being used in an air duct- now I'm curious. I would go with the pro insulated duct all day long if it's available.


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## oldsparky52 (Feb 25, 2020)

Thank you all very much. A lot of good information from this group, I appreciate it.


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## Bourbon County (Aug 19, 2020)

As CMP mentioned, the main objective to a bath exhaust is to remove the heat and humidity created by showering. Getting that heat and humidity out of the house makes a difference in your A/C system performance and overall comfort of your home. The one for the toilet or the proverbial "fart fan" is just a courtesy. 

There are a number of multi-point exhaust systems on the market, Fantech, Soler & Palau, Broan, and Panasonic all make those systems. Most offer the remote mount inlets available with light kits if you need the light. The downside to these is they're probably much more powerful than you need. For a toilet something in the 40-60 CFM range is quite adequate, if you can mount one inside the shower and use something in the 100-120 CFM range that will do a good job unless your shower is huge. The multi-point systems as well as the inline duct fans are usually in the 300-400 CFM range. 

I also agree with going with insulation wrapped metal duct if possible. Use aluminum duct and tape and mastic all the joints...


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## AK_sparky (Aug 13, 2013)

I agree, you don't want a P trap. What you do want is the duct to rise up higher than the point where it vents outside so that warm air doesn't rise straight out. When I did mine I just went up about a foot, then back down to where it vented out the gable vent.


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## HertzHound (Jan 22, 2019)

When I was just a few years in the trade, I installed a heat/light/vent combo at my mothers house. There was nothing there before. I don’t remember why, but I didn’t vent it to outside the day I installed it. No time? No hole saw? It was going to go out the soffit, so I left it there until I could return. Well I never got around to it. Years later she was having a roof put on. She had to have the sheathing replaced where the end of the duct was because it rotted out. Probably only took five years.

So I vented it out so it wouldn’t happen again. I went out the gable end. I used 4” round sheet metal duct the whole way. I pitched it do drain to outside for the condensation. I’ve seen that plastic flex duct fill with water in every sag across the rafters. I didn’t want that happening. I don’t do many fans. When I do they are usually “vented by others”. The few I’ve done since, I used hard duct and pitch it to outside. Even in my own house.


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## joe-nwt (Mar 28, 2019)

AK_sparky said:


> I agree, you don't want a P trap. What you do want is the duct to rise up higher than the point where it vents outside so that warm air doesn't rise straight out. When I did mine I just went up about a foot, then back down to where it vented out the gable vent.


In essence, you created a p-trap. Change in elevation = hot air can't rise out/ cold air can't flow in. Much better than relying on those chintzy back-draft dampers.


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## AK_sparky (Aug 13, 2013)

joe-nwt said:


> In essence, you created a p-trap. Change in elevation = hot air can't rise out/ cold air can't flow in. Much better than relying on those chintzy back-draft dampers.


Yes, I guess it is in inverted P-trap. I thought you were suggesting something like a plumbing p-trap that would leave a low point which could cause a problem with condensation being trapped and accumulated.


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## schreib (Apr 30, 2020)

oldsparky52 said:


> How far is too far to hit the gable (thanks for that, I like that idea). It's probably about 20' to the gable. I guess I could get a high cfm fan and upsize the duct to reduce drag. Any suggestions on this?


If you use flex it severely limits the airflow, LOTS of pressure drop. Best to use pipe as much as possible and minimize bends. This could allow you to keep the same fan in place too.


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## Johnkaw (Dec 16, 2020)

oldsparky52 said:


> I have never gotten around to replacing the non vented bathroom fans that were originally installed in my home. I was talking to a friend of mine discussing how I would do it (after I lost some weight) and how much I hated the idea and process of doing it.
> 
> Anyway, the discussion of venting came up and he was of the opinion that pointing the vent duct to the ridge vent would be fine. I know that's what a lot of people did in the early 70's, but ... IDK. My buddy (who is pretty sharp) said there would not be enough moisture to be a problem. I'm a little dubious about this since this practice was banned (where I worked) in the mid 70's.
> 
> I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


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## Johnkaw (Dec 16, 2020)

oldsparky52 said:


> I have never gotten around to replacing the non vented bathroom fans that were originally installed in my home. I was talking to a friend of mine discussing how I would do it (after I lost some weight) and how much I hated the idea and process of doing it.
> 
> Anyway, the discussion of venting came up and he was of the opinion that pointing the vent duct to the ridge vent would be fine. I know that's what a lot of people did in the early 70's, but ... IDK. My buddy (who is pretty sharp) said there would not be enough moisture to be a problem. I'm a little dubious about this since this practice was banned (where I worked) in the mid 70's.
> 
> I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


Hello 
By code you can terminate your bath vent through the roof or soffit with uninsulated 4 inch duct up to 15 feet. Hope that helps.. John


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## TheNorm (Jan 3, 2011)

oldsparky52 said:


> I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


I had quite forgotten about Electrician Talk as I was here way long ago then out of no place I get an email with this thread in it. Sparky, just my experience. I live in the south and have good ventilation in the attic. My bathroom fan exhausts directly to the attic....period. I was leery about at the time but that was several years ago and the roof hasn't caved in yet. Frankly, running a vent hose to the gable or something similar never occurred to me.Fair impossible since the crawl space closes so quickly. And no ridge vent. So...I went for it and it's fine. Whatever you do you'll much appreciate that fan.


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## dbrickles (Feb 4, 2020)

oldsparky52 said:


> I have never gotten around to replacing the non vented bathroom fans that were originally installed in my home. I was talking to a friend of mine discussing how I would do it (after I lost some weight) and how much I hated the idea and process of doing it.
> 
> Anyway, the discussion of venting came up and he was of the opinion that pointing the vent duct to the ridge vent would be fine. I know that's what a lot of people did in the early 70's, but ... IDK. My buddy (who is pretty sharp) said there would not be enough moisture to be a problem. I'm a little dubious about this since this practice was banned (where I worked) in the mid 70's.
> 
> I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


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## dbrickles (Feb 4, 2020)

Johnkaw said:


> Hello
> By code you can terminate your bath vent through the roof or soffit with uninsulated 4 inch duct up to 15 feet. Hope that helps.. John


Sir
You are correct when you stated it was an acceptable practice in the 70s. Depending on what state you live in and what code your state has adopted. The International Mechanical Code (IMC) requires that we discharge exhaust air to the outside of the structure, because of the moisture associated with the bathroom exhaust. An easy fix is to exhaust through the gable end, using a back draft damper. Hope this was helpful!
Crazycodeofficial61


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## MadSparky (Mar 2, 2018)

oldsparky52 said:


> I have never gotten around to replacing the non vented bathroom fans that were originally installed in my home. I was talking to a friend of mine discussing how I would do it (after I lost some weight) and how much I hated the idea and process of doing it.
> 
> Anyway, the discussion of venting came up and he was of the opinion that pointing the vent duct to the ridge vent would be fine. I know that's what a lot of people did in the early 70's, but ... IDK. My buddy (who is pretty sharp) said there would not be enough moisture to be a problem. I'm a little dubious about this since this practice was banned (where I worked) in the mid 70's.
> 
> I am soliciting comments/opinions on whether it is okay to just run the vent duct to the ridge vent of the roof, or am I asking for trouble if I do this?


Hi, it really depends on the activity going on in the bathroom. Is there a shower? Tub? Obviously long hot showers put out a lot of moisture. If you vent all that humid air to a cold attic (in winter) it will condense and accumulate on wood framing, causing mold and rot. Also, it could saturate your insulation, reducing R-value and possibly causing mold growth. I've seen it happen first hand.

Also, you'll want to use insulated ducting for bath vents passing through an attic. If you use uninsulated ducts, the steam will condense inside the duct and run back down into your bath van, possible causing water damage or damage to the motor or electronics.

Bottom line is there is a reason why we have building codes. Best to stick to them for your own safety as well as the safety of your property.


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## Ancient One (Sep 2, 2017)

When I was young, there were very few bathrooms that had exhaust fans. I started seeing them in the newer homes built in the late fifties. They dumped straight up into the attic space. Then there was the start of venting them out to the gable end vent, usually by metal duct. Then later on there was the advent of the flex tubing which way simplified vent runs. Being as all, and I mean all....... bathroom mechanical vents (exhaust fans) have a back flow built in. Therefore there has never been any reason to form a "P" trap or any other system of regulating exhausting fan flow.

Bath exhaust fans are only required in bathrooms that do not have a window opening to the outside. Sometimes in replacing a bathroom fan for clients I run across ones that were only dumping into the attic space. When installing the new fan I do vent it to the nearest attic whether gable end or roof mount. As I am in the south there is little need to insulate the vents and have so far never seen that done. But one needs to do what needs to be done in their own location. 

I always try to purchase vent fans for my customers which come on with the light and have very low sone ratings The lower the sone, the lower the noise. There are huge differences.

Just my way of seeing it and doing it.

J W


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