"I'll probably get yelled at for this, but I just put in a bathroom vent fan, and in my attic I have 2 roof vents plus an electric whole house attic fan that vents through the top (about 18" in diameter). Rather than cut another hole in my roof, I ran rigid 4" duct from the bathroom fan to just under where the attic fan is ( about 8 feet total duct). So far its working great."
One problem with this is that the attic fan is now likely drawing out air from your bathroom even when the bathroom fan is off. In summer, I would think a good deal of airconditioned air would go out this way.
" Through the sidewall or the roof. A poor third would be through the soffit, which may not be code locally. "
I don't know where venting a bathroom fan out the soffit is a code violation? Here in NJ most homes are done that way and we are about as regulated as it gets. I don't see anything wrong with doing a soffit vent.
What happens is that warm moist air is drawn into the next soffit vent into the attic space where it can cause damage. Remember that soffit vents are normally air inlets.
"What happens is that warm moist air is drawn into the next soffit vent
into the attic space where it can cause damage. Remember that soffit vents are normally air inlets. "
I guess that's theoretically possible, but has anyone ever seen it lead to an actual problem? Bathroom fans are almost always on for a short time, so any moisture that was introduced should dissipate pretty quickly. I have a hard time believing that in actual practice, this is really an issue. It's done on most of the homes here in NJ that I've seen and hasn't been harmful.
I've got the fan vented thru the soffit. In cold weather the vented air condenses quickly making it visible. It's quite obvious that it blows away from the house and does not get sucked back into the adjoining vent.
The point is why do it that way when there are better ways?
I don't know if there are documented problems when it is properly vented out the soffit, but it is common that someone will just put the vent close to a soffit vent and consider that proper venting. That has been reported as causing problems.
I have heard of a couple of cases where someone reported that even when properly venting out through the soffit there has been problems, but I am slightly skeptical of those so I would not say it has been documented. .
You are probably referring to the ventilation of combustion appliances in which case you have a valid point. But unless you are dealing with someone with extraordinary toxic farts the problem with a bath fan vent is not a issue worth worrying about. You are making a mountain out of a molehill.
When we had siding done a few years ago, I was not sure where a future exhaust fan would be mounted within the bathroom. An exhaust vent (a BuildersEdge product, special ordered from Home Depot) was installed in the soffit at that time. The vent, which has no moving parts, was centered within the span of the existing bathroom window; that bothered me for the reasons that you mentioned, Joe.
Recently had a contractor gut and redo our bathroom including the addition of a Panasonic FV-08VQL3 fan. He strongly urged me not to go through the roofline, (apparently because he was not a roofer). As it turned out, the fan was mounted within the wet area, which made it NOT inline with the existing vent. After some discussion about positioning of the flexible duct (I objected to having any bends in the layout of the duct), the existing vent was simply relocated such that there is a short and straight run of approximately four feet to the (relocated) vent in the soffit.
Going through the roof would have been agreeable with me. Not enough thickness to mount this fan within the vertical wall. The use of soffit vents is commonly used. The damper is within the fan assembly itself, not in the exhaust vent that is mounted at the soffit.
I have not been up on a ladder to test the air flow yet; but am hoping that the duct tape does not dry out and fall apart ...
I have a hard time believing that in actual practice, this
Ya know, last year I put two vents in through the roof. They don't cost much, don't take long and don't leak. It's just a bad ida to vent them in the attic period
So you put 2 holes in your roof and I didn't. Furthermore I vented out thru the soffit not in the attic. I hope your holes in the roof turn out better than your reading comprehension.
And thus my house is up to code and yours isn't. there is no difference between a vented soffit and the attic. I am happy that your insulation isn't soaking wet, but you won't be working on my house anytime soon. Hey, the gas furnace usually vents away from the house too, but you don't put it right next to the window.
Since I merely pointed out that it was not a big deal to put it through the roof, the same way that the soil stack does for the very same bathroom, an is not prone to leaks, I think it is your reading comprehension that is questionable.
Maybe a hole in your roof isn't a big deal. It is in mine. And you're absolutely correct that I won't be working on your house. I don't do business with assholes.
There does seem to be differing opinions on the subject. While I am inclined to believe that it is not a big problem, I would not want mine vented that way.
That is done on all new buildings here. I just took a picture of one today. Can I upload binaries here? Do you really think a slight U in a 4" pipe is going to fill up with water from the minimal amount of snow or rain that might get into the pipe? If you get that much water in there the trap is NOT your problem. You have other problems. If you do not put the "trap" there where do you think that water goes. Right into your fan, your motor and your grill (if metal) and causes rust.
That is not done here and I believe it is against code. The moisture in the winter builds up ice and causes problems in the soffit and with any wood in there.
OK A case in point. My parents house has 2 bathroom fans that vent into the attic, no ducting, just straight from bathroom to attic. On top of that her over the range vent ducted into the attic too. I was up there last summer doing the range vent properly through the roof because she was having a kitchen remodel done. I expected to see the buildup of 35 years of grease, I expected to see mold, I expected to see wood damage. To my surprise there was none of the above. I did vent the range properly, but left the bathroom vents. I am not saying you should do this but in there case it did not cause problems. There could be many reasons for this. It is a 2000ftsq ranch house with attached garage and attic all the way through with excellent ventilation. On my small 1000 ftsq hip roof house I'm sure it would cause a problem. I redid my bathroom in January and found that there was a complete 1" gap all around my masonry chimney from basement to attic (1953 house). This caused years of moist warm air to flow up this gap and be drawn into the attic in the winter. All around the chase the wood was rotten in the attic and needed replacement which was no problem as I had taken the masonry chase out and replaced it with a B vent.
I seem to recall, either in Fine Homebuilding or a CMHC publication that under certain circumstances in cold climates venting up through the roof can lead to thermosyphoning hot air continuously when the fan is off. Which wastes heat, and in a properly vented "cold" attic, can lead to condensation problems inside the vent line, resulting in water dripping from the fan and corrosion. In a previous home, we had exactly that problem on really cold days - sitting on the throne getting dripped on from above (no comments about below ;-)
In those cases, venting out horizontally through the wall, or down through the soffit was superior, because it won't thermosyphon.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.