# Noisy Flexible Vent Pipe From Bathroom Exhaust Fan?



## Chris Sweeney (Apr 21, 2012)

I just installed a new exhaust fan for a customer. I used the existing cheap 4" flexible piping (basically an accordion of aluminum foil). When I turned the fan on, boy was it annoyingly noisy. Actually, the fan itself wasn't noisy, but the fluttering of the flimsy, paper-thin flexible ductwork was where the noise was coming from. I ended up changing the vent pipe to rigid pipe and the noise went away. 

Anyway, this was the first time I have experienced this. Have any of you had this experience with cheap flexible vent pipe making noise before? If so, how did you go about fixing it? Could I have used just a better quality flexible vent pipe as opposed to using rigid?

Thanks!


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## J L (Nov 16, 2009)

I use rigid and make sure the pipe slopes down towards the exterior so any condensation runs to the exterior of the home


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## Steve57 (Feb 17, 2013)

I've been using insulated flex. It's quiet and should eliminate condensation.


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## The Coastal Craftsman (Jun 29, 2009)

There's few different types of aluminum flexible duct. The type you used and the more ridged type which can be stretched out but it's much more ridged. The type you used makes a lot if noise but the more ridged type makes no noise.


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## jkfox624 (Jun 20, 2009)

Or you could do what it seems everyone around here does. Just let it dump all that moist steamy air into the attic.


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## The Coastal Craftsman (Jun 29, 2009)

jkfox624 said:


> Or you could do what it seems everyone around here does. Just let it dump all that moist steamy air into the attic.


That works well. It helps defrost the ice on the roof :laughing:


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## jkfox624 (Jun 20, 2009)

BCConstruction said:


> That works well. It helps defrost the ice on the roof :laughing:


Plus a house isnt complete without mold. Helps boost your kids immune system. Damn sissies anyhow with all their flu shots and antibacterial soap.


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## Tinstaafl (Jan 6, 2008)

Chris Sweeney said:


> I used the existing cheap 4" flexible piping (basically an accordion of aluminum foil).


That's barely suitable for a 3-4' run of dryer vent; definitely not for a bath vent. You should be using insulated, preferably rigid. :thumbsup:


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## tenon0774 (Feb 7, 2013)

Schedule 40.

No grooves for moisture to get trapped in, an the fireman will thank you later if the place ever burns down. :jester:


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## ASInsulation (Aug 25, 2010)

RemodelGA said:


> I use rigid and make sure the pipe slopes down towards the exterior so any condensation runs to the exterior of the home


Sarcasm??? I hope....


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## tenon0774 (Feb 7, 2013)

ASInsulation said:


> Sarcasm??? I hope....


:blink:
Why would you say that?


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## J L (Nov 16, 2009)

ASInsulation said:


> Sarcasm??? I hope....


No sarcasm. A vent fan pulling hot moist air will form water drops in the pipe and I'd rather have those drops end up outside than back in the fan.


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## ASInsulation (Aug 25, 2010)

you pitch it up and out, and insulate the vent pipe. the purpose is to get the moisture out before it condensates. if you pitch it down, the moisture is now trapped at the high point of the pipe and you are essentially creating the condensation. maybe it will drip out the soffit or gable end where you lead it to, but why not get it outside the house before it gets to that point?


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## J L (Nov 16, 2009)

ASInsulation said:


> you pitch it up and out, and insulate the vent pipe. the purpose is to get the moisture out before it condensates. if you pitch it down, the moisture is now trapped at the high point of the pipe and you are essentially creating the condensation. maybe it will drip out the soffit or gable end where you lead it to, *but why not get it outside the house before it gets to that point?*


I didn't say to do loops around the attic with it. I take the most direct route out not including the roof as I'm not a fan of additional roof penetrations. 

Have you ever taken a shower and noticed the paint above the shower surround has condensation built up on it? Well the same thing is happening within the vent pipe - you're taking all of the moisture and running it through a small duct. It's going to condensate. So you might as well plan on dealing with that condensation. And I'd rather have the condensation go to the exterior of the home and out a vent than to have it come back into the fan unit and/or the drywall around the unit.


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## tenon0774 (Feb 7, 2013)

RemodelGA said:


> I didn't say to do loops around the attic with it. I take the most direct route out not including the roof as I'm not a fan of additional roof penetrations.
> 
> Have you ever taken a shower and noticed the paint above the shower surround has condensation built up on it? Well the same thing is happening within the vent pipe - you're taking all of the moisture and running it through a small duct. It's going to condensate. So you might as well plan on dealing with that condensation. And I'd rather have the condensation go to the exterior of the home and out a vent than to have it come back into the fan unit and/or the drywall around the unit.


Well put.

I think Mike Guertin did an article in Fine Homebuilding about this years back.

I've used pitched, solid pipe ever since.


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## ASInsulation (Aug 25, 2010)

go back to these houses in a few years. if you are venting these to a soffit or a gable end vent, which are designed to maintain airflow in the attic(assuming they are functioning properly) they will draw the moisture back in of whatever makes it out that doesn't condensate. many times this will cause mold on the sheathing in the bay the fan hits the soffit, or dry rot. 

There are instances it would be practical, but in most cases, i'd terminate the moisture outside rather then the water. It's also mandatory in the Home Performance with Energy Star program to do this with an upward pitch of a minimum 1" per 4'. But either way. I make alot of money re-routing these vents and insulating them, so no complaints here!:thumbsup:


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## tenon0774 (Feb 7, 2013)

ASInsulation said:


> It's also mandatory in the Home Performance with Energy Star program to do this with an upward pitch of a minimum 1" per 4'.


I was wondering why you pitched them that way.

unbelievable...Energy Star


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## ASInsulation (Aug 25, 2010)

*Have you ever taken a shower and noticed the paint above the shower surround has condensation built up on it? Well the same thing is happening within the vent pipe - you're taking all of the moisture and running it through a small duct. 
*

Only when the moisture has no release. If the vapor can continue to travel up without reaching a temperature to create the condensation, it will do so. however, the soffit method is essentially TRAPPING the vapor to condensate in the pipe. The vent pipe should be working just like your chimney with concerns to draft. Same building principles at work here.

If you vent properly through the roof, there should never be an issue.

If you vent properly(assuming CFM and duct size are proper), and you use the soffit vent that is also working properly, you might as well just let it vent into the attic. Gable end release does seem a little more practical, so long as the termination isn't anywhere near the gable vent.


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## J L (Nov 16, 2009)

I don't recommend going out existing attic ventilation passages in the gable end or soffit. I recommend using a proprietary vent for the bath fan which can exit out the side wall of a house or in the eaves.

So what you're saying is that because you wrap the pipe in insulation, even though the duct runs up through a 20° attic, that the insulation will keep the duct warm so it won't condensate? That duct and insulation are both at 20°, the same temp as the attic. Again, creating the perfect situation for condensation when combined with hot humid air.

You have your methods, and I have mine.


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## pricemech85 (Mar 13, 2013)

I would be sure to use snaplock pipe in any and most cases of running vent pipe. It cuts down on noise as well being much easier to clean out.


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