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Old 10-30-2008, 07:48 AM   #1
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Bathroom Fan Dripping


Hi guys... this is my first post, and I'm as frustrated as ever. I hope someone here can help with my situation. The previous owner had our bathroom fan venting directly into attic. I know this is terrible, so I installed a roof vent and connected it to my bath fan via flexible ducting. I felt pretty good after finishing this project until I noticed water (condensation) dripping back through the fan. Per askthebuilder.com, I re-ran the ducting using 4" galvanized ducting with (2) adjustable elbows, one at about 80 degrees the other at about 10 degrees between the fan the roof cap. The total length of the run is about 3.5 feet max. I insulated the duct with spray foam as instructed. Unfortunately, I still have condensation coming back into the bathroom. I suspect that condensation is collecting on the flapper in the roof cap and then dripping back down the duct, but I'm not positive of this. When I was up in the attic replacing the flexible duct, I noticed a lot of condensation on the flapper, but I hoped that it would go away with the upgraded ducting and insulation. The roof cap that is in the roof now is from a cheap kit that I bought at Home Depot. Is there a particular roof cap that works better than any other? I would consider venting through the soffit, but space is extremely limited in my attic. I suppose I could vent though the gable, but my duct run would be about 15-20 feet. Does anyone have any suggestions? Thanks!

Oh yeah... I live in Mid-Michigan, so it gets pretty cold this time of year, which I suspect is why I'm having the condensation problem.

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Old 10-30-2008, 08:04 AM   #2
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Bathroom Fan Dripping


When I read the title of this thread I figured..."They need to insulate that vent." You've done everything I would have suggested that you do!

The galvanized vent won't do anything to prevent condensation, but it is a fine material for this application. You say you already tried insulated flexible duct?

You might go ahead and try venting through the soffit to reduce the slope of the pipe back toward the fan...Resulting in the dripping. There's always going to be at least some condensation in your climate (especially during cold weather), so you just have to find a way to minimize it and manage it.

You might get some flexible duct and slide it over the galvanized vent. Insulating with spray foam is a little unconventional.

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Old 10-30-2008, 08:48 AM   #3
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Bathroom Fan Dripping


I would put a loop in the ducting like a drain pipe trap.
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Old 10-30-2008, 09:14 AM   #4
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Bathroom Fan Dripping


The original ducting that I installed was cheap flexible coil duct without insulation. I have not tried flexible duct WITH insulation.

I agree, the expanding foam was unconventional, not to mention inconvenient, messy, and difficult. Four days later and i'm still picking a layer of foam off my hands. I may try adding some regular fiberglass insulation around the duct next time I'm up there.

I really think that a different style roof cap may solve the problem. The current roof cap has a flapper that is angled such that accumulated condensation will run back down the duct. This seems like a poor design. I already know for a fact that the roof cap is very restrictive because our bathroom fan isn't nearly as effective now as it was before. The vent that I'm using is like the one in the attached image, except mine is steel. Unfortunately, I think I will need to change this vent regardless, since it will undoubtedly become buried in snow within the next month or two. I hadn't even considered snow when I was installing this thing.

I will try a different vent cap first. If that doesn't work, I'll have to see if there's enough room to get a duct to my soffit.

Thanks for the reply.
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Old 10-30-2008, 09:18 AM   #5
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Bathroom Fan Dripping


I thought about your idea Mikey, but that would simply allow standing water to collect, and restrict air flow... both of which are not good side effects. Eventually, the water "trap" would overflow anyway leaving me with the same problem. In winter it would freeze and be even worse I presume.
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Old 10-30-2008, 02:10 PM   #6
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Bathroom Fan Dripping


Your getting condensation because of the metal duct. The Big boxes sell flexible insulated duct in 4", 6" and 8". Using that should eliminate the issue.
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Old 10-30-2008, 02:15 PM   #7
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Bathroom Fan Dripping


Agreed, putting a trap in it is definately not a good idea. Plus, it would hinder the fan's performance.

The condensation will happen with any sort of duct, but can be worse with metal if left uninsulated. Warm humid air going into a cool attic will result in condensation in any duct material.

Nothing beats an insulated duct and a good powerful fan. The $40 cheapies won't do a good job no matter what you do.
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Old 10-30-2008, 03:22 PM   #8
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Bathroom Fan Dripping


Also run the fan longer so it's still not hot steamy air trapped in the duct when you shut the fan off. I put a timer on mine so it will keep running after I leave the shower but won't run all night.
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Old 10-30-2008, 04:48 PM   #9
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Bathroom Fan Dripping


I did not mean to put a trap in it, just form the ducting in a loop like a trap. I install the ducting coming from the fan let it drop to the ceiling and then up to the roof. The moisture is coming from the bathroom so the ducting will always get damp, if it the ducting is heading straight down, of course the moisture will follow the ducting. Running the fan longer will help but not stop the dripping.
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Old 10-30-2008, 05:04 PM   #10
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Bathroom Fan Dripping


Quote:
Originally Posted by mikey48 View Post
I did not mean to put a trap in it, just form the ducting in a loop like a trap. I install the ducting coming from the fan let it drop to the ceiling and then up to the roof. The moisture is coming from the bathroom so the ducting will always get damp, if it the ducting is heading straight down, of course the moisture will follow the ducting. Running the fan longer will help but not stop the dripping.
Wouldn't the result be the same, water trapped in the low area? It wouldn't evaporate in that environment before the next shower occurred.
Eventually the water would leak out.
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Old 12-05-2008, 10:47 AM   #11
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Bathroom Fan Dripping


Well, it's been a little over a month since I posted this topic. Over the last few week we have dealt with the problem by simply not using the fan, but even then the water would leak at times.

This got me thinking that the problem may not be with the duct or roof vent like I had suspected. Sure enough, when I took the fan grill off for inspection, I see that there is plenty of condensation on the inside of the fan housing itself. As it turns out, with all of the effort put into insulating the duct, I forgot to put insulation back over-top of the fan housing in the attic.

After insulating over the fan housing, and just for good measure, using the same roll insulation with zip ties to further insulate the ducting, the problem is SOLVED!!!

THanks for everyone's input
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Old 12-05-2008, 09:12 PM   #12
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Bathroom Fan Dripping


I'm glad you solved your problem mntnbkr. As soon as I'm sure I have my attic sealed and vented properly, (I have to find out if I packed the insulation in too tight under the baffles/over the wall top plate) I'm going to hire someone to do the same thing you've done. My bathroom fan was venting under the insulation covering the fan housing. Duh!

I'm wondering if anyone has any suggestions as to what questions I need to ask the guy who might be venting it up through the roof/blowing-in the insulation.

After reading this post I'm thinking about asking him what products he'll be using. Then, if you don't mind, could I ask you guys if it's the same products you would use? I really don't want to learn the hard way that he used cheap products.

Is it pretty typical for a guy who does insulation to also do this kind of venting or should I get a roofing guy? He also said he will put another roof vent in for hot air to leave the attic because there are only two up there now.

I'll just bother you with one more question. Has anyone ever heard of bringing the hose from the 'blown-in insulation machine' through a vent in the roof? He said that they remove one of the roof vents and bring the insulation in that way. It avoids having to leave a door or window open, letting cold air in the house, and keeps the mess outside. That makes a lot of sense, but I can't imagine anyone being thin enough to fit through one of those vents. Would it damage the roof or shingles to remove a vent, climb in and out of it and have the hose rubbing against the shingles?

Thank you.

Barb
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Old 12-06-2008, 12:08 PM   #13
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Bathroom Fan Dripping


Our home was built in 2004 and we had the same trouble last winter when it hit -30C to -40C. I believe they did the loop trick mentioned above. It works, vents, doesn't leak and I have no reason to go in the attic.

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