Installing a bathroom exhaust fan and the proper way to vent it...

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All,
I need a little advice from those that have installed bathroom exhaust fans and the proper way to vent them. I am in the process of deciding if I should just vent the fan into the attic or cut a hole/holes in the soffit and have the ducting terminate at this opening. One other option is to install a pvc T fitting in an existing plumbing vent and have it vent through the roof. Is the last method acceptable in most areas as far as the building codes?
If I drill 6 or 7 1/2 inch holes in a 4'' diameter circle through the aluminum soffit and tape the end of the fan duct to the soffit at this location, will thismethod be sufficient to vent the fan? The problem I have is that the roof line is about 35-40 feet high so the only way I can access the soffits is through the attic.
thanks
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None of these methods is really acceptable. Venting into the attic is right out, you need to remove the moisture from the house. I'm sure venting into a plumbing vent is forbidden, you could conceivably get sewer gases coming out the fan vent. Venting through the soffit is allowed, but it is not really a good idea, because some of the moisture will migrate back upwards, condense on the soffit, etc.
The two good options are (1) vent through the roof and (2) vent through the sidewall, at least 3' below the soffit and at least 4' horizontally from any operable windows.
Cheers, Wayne
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On Fri, 11 Nov 2005 13:43:54 -0600, Wayne Whitney

I suspected that these would be better solutions, however, they are both problematic in my case. The sidewall is made of brick and I do not want to punch ar hole in my roof unless it is absolutely necessary for obvious reasons. I really do not want another 4 inch pvc pipe sticking out of my roof. The bathroom is on hte front side of the house.
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The usual roof termination for a bathroom exhaust fan is quite short, it's not an exposed pipe. An exposed pipe would allow rain into the vent, a bad idea. [Doesn't matter for the sewer, though!] See, for example <http://www.broan.com/display/router.asp?ProductID )25>.
Cheers< Wayne
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On Fri, 11 Nov 2005 14:33:24 -0600, Wayne Whitney

Thanks. I didn't realize that these were available.
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Venting into the attic will/may cause condensation. Code violation.

This will work providing you install a soffit vent to keep the critters and insects from coming in. There are vents made for this application.

Not acceptable in any areas and extremely dangerous due to sewer gas entering the room.
Code violation.

No. Vent must be free flowing, imo.
--
TimL


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No no no!
Unless you like mold having a nice damp place to call home in your attic.
I had two of these corrected on my current home when I purchased it. They are now properly vented with roof caps. The soffit thing might work too.
-- Todd H. http://www.toddh.net /
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On 11 Nov 2005 14:12:37 -0600, snipped-for-privacy@toddh.net (Todd H.) wrote:

I forgot to mention that the attic is well ventilated just with the existing soffits and ridge vent. Everytime I go up there, I can feel a slight breeze. I've always been puzzled as to how this would cause a moisture problem in the attic. After all during a rainstorm, the air that gets pushed through the soffits is loaded with humidity. I'm sure it's at least 90%.
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Regardless of the attic breeze or no, you don't want to vent into the attic--if for no other reason that most home inspectors will flag it in a heartbeat, regardless of how much ventilation. A roof cap is the way to go.
-- Todd H. http://www.toddh.net /
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Jim-
Where is the house?
In my previous SoCal home both batroom fans had their flex aluminum ducts terminate near / against the gable end attic vent
I never had any mositure problems but SoCal is near desert conditions.
If you're in an area where condensation could occur make sure you do it right. You will be buying a lot more trouble downstream
The "correct way" is a roof penetration. The soffit solution is ok as well, as long as the flow terminates with an acceptable "vent cover".
cheers Bob
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The house is in Virginia. The winters are relatively mild. Certainly nothing like Minnesota or New England. Temps rarely stay below freezing. The end of the flexible aluminum duct was just laid on top of the soffit.
What I will probably end up doing is to extend the ducting upward until it is within a few feet of the ridge vent. There's just me living in the house and I rarely take long, hot showers.
Also, how critical is it that the fan be installed level and plumb for proper operation? I installed it a bit out of level.
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Jim wrote:

The instruction manual on the Broan vent fan I put in says put on a ceiling with no more than a 12/12 pitch. I am not sure what that means, maybe 12" of pitch for every 12 feet? Maybe someone else knows. I think its for proper operation of the damper.
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Same units for rise as run, either 12"/12" or 12'/12'. NOT 12"/12'.
45 degrees. 100% grade, Pii/4 radians from horizontal.
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Well then, if there's enough room up there, then how about just routing the exit duct out the rear roof instead of on the front? You want 'as little ducting as necessary' though. Otherwise there are plenty of low-profile roof vents than can either be found in closely matchig color to your existing roofing material, or painted to blend in.
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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. I know this is still not the right way, but at least I routed the vent close to where the opening in the roof is. Some people just let the fan vent in the attic, and letting it gradually find its way to the vent in the roof.
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One thing I'm starting to learn the hard way (now that my wife is selling real estate) more buyers are requesting home inspections ...and some communities are requiring it ...before they buy. Inspectors are finding things the current occupants have juryrigged. Sometimes if the list is long enough, it kills the deal. Other times the seller has to have the stuff corrected. I'm lucky I haven't done a lot of these kinds of things (but have done a few) but it sure opened my eyes. I'm tending to do things the right way lately. Just a caution.

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"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.
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What everyone else said. Plus: you run the flexible duct into the soffit. Flexible vinyl duct is much better to use for ease of installation in this instance. (Does not apply to dryer venting.) Use a powerful drill with a 4-1/4" hole saw to drill a perfectly round hole into the soffit. It is best to use a "hole-hog" with an offset clutch for this job. A regular drill can pull you right off a ladder if the hole saw binds up in the hole which is very likely with a 4" hole saw. You must cut the hole from outside. You should hire a carpenter/handyman to do this if you are not comfortable on a ladder that high. You pull the flex duct out of the hole while out on the ladder. You then use a standard 4" round aluminum soffit vent to tape to the flex duct after stretching it over the inner ring. Push the flex duct back into the hole until the round vent is flush and secure with a couple of brass brads. Usually best to drill a couple of tiny holes for the brads while on the ground. Easy as pie. Alternative: Use a roof vent. Requires you to get up on the roof and do some shingle re-work. I hate these. They are an eyesore and are an invitation to leaking, especially in cold climates.

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Use insulate flex ducting to prevent moisture condensation and put a U in it so that any water that might get in the pipe through the top of the vent does not drain back into your fan.

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Flex ducting in addition to putting a U in the ducts puts more resistance on the flow being discharged from the fan which impedes its performance. In addition, any "trapped" water in that U would also put resistance on the flow.Putting in rigid duct with minimum bends would decrease the chances of the ducts sweating since it will exhaust better. In my opinion, if you leave the fan on for even 5 minutes after a shower it would be enough time for the fan to clear the bathroom of humid air and by the time the fan is turned off, the likely hood of moisture in the duct will have greatly decreased.
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