bathroom exhaust vents

lishinFebruary 1, 2011

Hi,

My contractor connects two bathroom exhaust ducts into one roof opening, like the picture below:

Is there any problem with it? His reasoning is trying to reduce number of roof penetrations.

Thanks,

Alan

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mike_home

I don't buy the logic. What difference if is is one larger penetrations versus two smaller ones.

Are these 6-inch ducts? I see a lot of daylight around the hole in the roof. How is this going to be capped?

I have two bathroom fans connected to separate 6-inch ducts. For each one, a 6 inch round hole was cut into the roof. There is a roof cap on each. The cap has a 6 inch round metal piece which comes through the roof. The flexible ducts are attached to this. Roof caulking is used to make it waterproof.

I suggest you added insulation to each vent. This will prevent moisture building up inside the duct and dripping back onto the exhaust fan.

    Bookmark   February 2, 2011 at 11:29AM
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lishin

I have a total of 5 exhaust fans. 4 of them are connected like this (2 large openings plus 1 small one with only 1 duct). They all are 4" ducts. I only see the metal roof jacks used. What should we do to fix this now? Contractor only mentioned about spray foam around the gaps.

Thank you!!

    Bookmark   February 2, 2011 at 12:51PM
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lishin

Forgot to mention that the location is San Jose CA area. How important is it to insulate the bath ducts here?

    Bookmark   February 2, 2011 at 12:59PM
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mike_home

How is the contractor going to ensure the roof doesn't leak? I have never seen spray foam used to seal a roof connection. I am not expert, but I would be nervous if this was my roof.

How cold does your attic get in the winter? You may not have a condensation problem. You should ask the contractor about the normal practice in your area.

    Bookmark   February 2, 2011 at 1:27PM
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weedmeister

In San Jose, I wouldnt think that insulating the ducts is necessary.

I have something similar to this on my roof. Not a problem as long as the cap used is big enough. There is no cap here in this picture, hence all the daylight.

    Bookmark   February 2, 2011 at 2:12PM
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kframe19

Personally I think the fewer penetrations through a roof the better.

I also don't see anything inherently wrong with venting two bath fans through a single roof opening.

Even if both are on at once, probably the worst thing that will happen is that they back pressure each other and they don't vent quite as efficiently.

Both of my bath fans are vented through the same soffit vent.

    Bookmark   February 2, 2011 at 3:58PM
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lishin

I am concerned about the cap that you all mentioned. This is what I have now:

Those two on the left are bath vents.
There is no round metal piece for the duct to attach to. Is this good enough?

    Bookmark   February 2, 2011 at 4:35PM
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lishin

Anyone else has more suggestions or comments?

    Bookmark   February 10, 2011 at 10:23PM
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weedmeister

I have a square ventilated cap. The duct does not need to attach directly to the cap.

    Bookmark   February 10, 2011 at 11:54PM
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jaysgarden

So the flex ducts you have pictured in the first picture are both terminating into which roof vent in the 2nd picture?

    Bookmark   February 11, 2011 at 7:02AM
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lishin

Right, those two flex ducts both terminating into the left most roof vent in the 2nd picture. There are two more ducts going into the middle roof vent...

    Bookmark   February 11, 2011 at 1:33PM
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showerq

I was planning on doing a similar thing, but I would join the vents from 2 fans in adjacent rooms with a Y connector so the two would merge into one and there would only be one duct exiting. Is that a workable solution?

    Bookmark   February 12, 2011 at 9:10PM
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lishin

I read somewhere here that joining ducts from two bathrooms may not be a good idea because the two bathrooms will be 'connected'?

    Bookmark   February 13, 2011 at 3:33PM
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