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Old 11-06-2011, 11:05 PM   #1
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What is the proper vent cap for bath/kitchen fans


I had my roof redone in spring and asked them to put a bath vent cap on as I was installing a new bath fan. They put a low profile vent cap on that looks like an upside down cake pan (approx 2-3" high). I questioned them about this as I assumed it should be a "goose neck" style but they assured me the low profile was the best. I thought they should know being the 'roof experts'.

Today was the first significant snow fall of the year. My roof and gutters are full of snow. I noticed the snow melted around the bath vent cap. The warm moist air from the bathroom is being forced up the duct to the cap. As it hits the inside of the "upside down cake pan" low profile roof cap, it gets redirected downward directly onto the shingles. The snow melts and the moisture runs down the shingles to the gutter which is already full. The water is dripping over the gutters and creating icicles hanging down from my gutters. I live in Saskatchewan, on the parries. Winters are long, cold and lots of snow. Today is the first day of snow, what's going to happen after 4-5 months of winter. Is the build up of ice from the melting snow going to cause water damage to my roof? Which is the correct vent cap?

Was I correct? Would a "goose neck" style of vent be better than a low profile/flat upside down cake pan type. My thinking is that the moist hot air would be blown out of the vent at 8", 10 or 12" (not sure of the height) above the singles into the air (not directly onto the singles). My thinking is that a goose neck style wouldn't cause all the melting of the roof snow and in turn not create icicles off the gutters. I don't know what I should do. I know the roof guys will change it if i ask. Am I just being paranoid? Is this normal? Is this correct? What a low profile the proper vent? Can anyone provide information and guidance as what I should do.

Thanks
Garth
Regina, Saskatchewan, Canada

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Old 11-07-2011, 03:32 PM   #2
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What is the proper vent cap for bath/kitchen fans


Could you safely take a picture of the vent that is being used?,,,,then post the picture?

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Old 11-07-2011, 03:40 PM   #3
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What is the proper vent cap for bath/kitchen fans


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Originally Posted by Roofmaster417 View Post
Could you safely take a picture of the vent that is being used?,,,,then post the picture?
From your description of the vent,,,,,it sound like a regular vent for attic ventilation was being used rather than a baffled damper vent.
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Old 11-10-2011, 09:06 AM   #4
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What is the proper vent cap for bath/kitchen fans


You want a "bathroom flapper vent". It has a flap inside that keeps cold air from getting in. Right now with just a roof vent covering your bath fan hose, cold air can run down that hose when the fan is off. So if you have a shower, and the hose fills with steam/moisture, what do you think will happen when the fan is turned off and cold air enters the hose?


If you have an accordion type fan hose:
Also, try and make sure your hose is as straight as possible from the fan to the flapper vent, just to prevent any moisture sitting in the ribs of the accordion hose.

This page shows a good diagram of a flapper vent
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Old 11-12-2011, 12:06 PM   #5
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What is the proper vent cap for bath/kitchen fans


I can't get on the roof at this time because of snow and ice etc. I did find some pictures on the internet that best resembles the vent cap I have. The one they installed does have a damper on it as does my bath fan housing. Is this the proper vent cap for a bath fan? I don't know. I do know that the one now is basically venting the warm moist air our the opening around the bottom outside edge of the vent can which is only about 3/4" (just enough to slid you fingers under) off the roof deck/shingles. The moisture and melted snow from around the vent is running down to my gutter (about 3' away), and is now going over the gutter and creating icicles. We've only had snow for a week and this is happening already. Will this not create an ice dam as the winter continues causing the water to be forced under the singles creating further problems? I assumed the vent cap should be a "goose neck" or "chimney" style where the vent opening is 8-12" above the roof deck/shingles. What are your thoughts? How do I find out what is the correct style, or is what I have now correct?
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Old 11-12-2011, 12:49 PM   #6
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What is the proper vent cap for bath/kitchen fans


Thanks bcdemon. There are two parts to the vent cap. The first is the part that the hose attached to, much like the adapter collar part in the link you sent. It is installed 'into' the roof deck. The second part attaches to the first and would be like the brown is to the black on the link you send. I do like the duel flapper idea although it seems the air would be once again forced directly, although not nearly as much, onto the roof deck. Do you use this style? Do you have problems with freeze up in winter?

Here is a link of the style I assumed would be used:
http://www.primex.ca/large_products/...tdoor/RV28.htm
or the smaller version:
http://www.primex.ca/large_products/...tdoor/RV20.htm

Thoughts?
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Old 11-13-2011, 05:28 PM   #7
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What is the proper vent cap for bath/kitchen fans


RoofMaster, I've managed to get some pictures of the vent. Thanks for taking a look and for your input.
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Old 11-14-2011, 09:44 AM   #8
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What is the proper vent cap for bath/kitchen fans


[QUOTE=michega;769448]Thanks bcdemon. There are two parts to the vent cap. The first is the part that the hose attached to, much like the adapter collar part in the link you sent. It is installed 'into' the roof deck. The second part attaches to the first and would be like the brown is to the black on the link you send. I do like the duel flapper idea although it seems the air would be once again forced directly, although not nearly as much, onto the roof deck. Do you use this style? Do you have problems with freeze up in winter?


or the smaller version:
http://www.primex.ca/large_products/...tdoor/RV20.htm

The RV20 is what we use around here ALL THE TIME. And no, there is no real issue with freeze & thaw in the winter (Kamloops, BC). They will melt the snow in front of the vent, but not enough to cause any issues. The only thing I have had to repair on these is one subdivision put the accordion type hose horizontal across the house to exit out the backside of the house. The moisture that got trapped ended up freezing inside the hose. That's why you should have the hose straight up and out from the fan to the flashing.
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Old 11-18-2011, 11:13 PM   #9
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What is the proper vent cap for bath/kitchen fans


I am in Calgary and my roofer installed the same vents for my bathroom exhaust. It is essentially an attic vent with with and insert that snaps in the bottom with flapper. I have found it to be quieter (I used to hear noises from outside through the vent) than the other type on my roof but since the temperature has dropped below zero, the flap has frozen shut and running the fan does not thaw it out when it is colder than about -2 deg.C because there is no air movement. I only found this out after going into the attic and discovering that the roofers had not properly re-attached the duct to the vent cap. With the flapper froze shut, the bathroom vent was venting into the attic. I am curious if you have the same problem with a frozen flapper. I think this type of cap is more prone to ice build up inside because the air has to work its way up and out of the vent cap instead of being directly blown out like the traditional design.

I plan to give my roofer a call and complain about the vent cap but maybe all vent caps with flappers have the problem of freezing up?

I don't know if you will find one that does not melt the snow on your roof. Most I have seen are low profile.

If you want to know why it is important to make sure the duct work is sealed properly to the fan and vent cap read here is my experience from last year.

The old vent cap had a fairly heavy flapper and although the duct was loosely connected to the cap, the resistance from the flapper (maybe it was frozen too) allowed the air to go into the attic instead of out the vent cap. (The previous home owner had replaced the caps shortly before I purchased the home, and the installers apparently did a poor job). You will know if your house is leaking moist air into the attic if the tips of the shingle nails poking into the attic attic have ice balls (not icicles) attachd to them. Consequently, I had a big mess in the spring when it all melted and had to replace the ceiling in my bathroom and some other places in the house. This is why I checked to see if the roofers had properly re-attached the ductwork, and guess what.. they had not. I would have had the same problem this winter.

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