Another Bath Vent to Roof Question


  #1  
Old 03-25-06, 12:05 PM
C
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Another Bath Vent to Roof Question

Hi,

I've scanned this forum for information and found it useful. I have a question that I haven't seen yet though.

I've installed a vent fan in a bathroom that formerly did not have one. Now I need to do the duct work.

There is already a vent in my attic--it's just a weather cap, with no fan or ductwork connected to it. I'm wondering if I can route whatever vent pipes I attach to my vent fan up to that existing weather cap? If I did this, I suppose I would have flexible ducts connect to the fan for a foot or 2, then have rigid, horizontal ducts to go under the vent, then an elbow, then another rigid duct up to the roof vent. I suppose if I did this, the vertical duct would run to the roof exterior level, or slightly above, but below the weather cap.

Is there any problem with this?

Also, I think I read I should use aluminum ducts. Is that correct?

Thanks,
chris
 
  #2  
Old 03-25-06, 04:22 PM
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cfree, Welcome to the DIY Forums.
There are a couple reasons not to do that. One is that the moisture will cling to the roof vent and drip down into the attic. If you live in a cold area, the moisture will freeze in the winter and you'll have ice hanging down into the attic. You will also have cold air blowing back into your bathroom since there will be no damper. Using metal ducts is preferable since you have moisture and most plastic ventpipes are corrogated. The water hangs up in the corrogations and does not exit. Most bath vents are aluminum. Good luck.
 
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Old 03-26-06, 07:03 AM
C
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Thanks for the feedback.

One follow up question about the damper you mentioned. Are you saying that if I add a new fixture, that fixture should have a damper? I'm not familiar with which kind of roof fixture I should use.

I ask because there is a damper on the fan unit itself that allows air to be blown out, but closes for air coming in.

thanks,
chris
 
  #4  
Old 03-28-06, 11:04 AM
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Yes, most fans do have built-in backdraft dampers, and they usually work pretty well. It's up to you if you want a second one at the roof jack, as it will add some extra resistance to airflow.
Broan has the roof jacks you need. Just go to www.broan.com and look under fan accessories. Most larger home centers will have them in stock.
Good luck!
 
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Old 03-28-06, 07:55 PM
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Thanks Andy and Majakdragon. I appreciate your help. I think I have the info I need now.

chris
 
 

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