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Old 10-21-2011, 09:24 AM   #1
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Double wall gas vent pipe?


Oh my home, a lot of work done before I bought it was done rather poorly. One example is the ceiling and water heater vent pipe. There is a HUGE gap and a very poorly hole cut hole for the vent pipe with an insane amount of space around it. There is a flange piece on the attic side of the ceiling which doesn't do much good.

I suspect it is single wall vent pipe. I can't even find any double wall vent pipe on Lowes or Home Depot's websites. Where the heck do you even get it? Or is all type B double wall?

Also what could I do to fix the horribly cut hole around the pipe? Heck I'm almost thinking about hanging some curtains or something from the ceiling around it. The water heater is contained inside of a cabinet with a cabinet space above it, so the top of the cabinet is only a couple of feet from the ceiling. Some custom made curtains would do nicely to hide the ugly hole cutting work, but first I need to address the vent pipe situation so I can seal around it somehow with wood or something. Maybe I can put wood around it on the attic side and fill in the hole with dywall repair on the other side so it doesn't look so bad and will seal up properly.


Last edited by Cubey; 10-21-2011 at 09:28 AM.
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Old 10-21-2011, 09:41 AM   #2
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Double wall gas vent pipe?


I had to call and order it from my local Lowes. IIRC, it took about 2 weeks for them to get it and cost about $20 for 2'.

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Old 10-21-2011, 09:44 AM   #3
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Double wall gas vent pipe?


Is there any way to tell if it's already there by looking at it without removing it?
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Old 10-21-2011, 09:45 AM   #4
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Double wall gas vent pipe?


Push on it. It's much stiffer than regular vent pipe. BTW, you could probably also get it from a true HVAC shop that may have it in stock.
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Old 10-21-2011, 09:53 AM   #5
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Double wall gas vent pipe?


It feels very thick, I can't even push it in any.

Here is what I have to work with. Oh, and the top of the cabinet is only about a foot from the ceiling.



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Old 10-21-2011, 10:04 AM   #6
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Double wall gas vent pipe?


Ok, it is double walled. I removed the old duct tape in the photo you see and seperated the pipes (they were barely attached anyway, hence the crappy duct tape job). So I should be safe sealing around it with sheet rock, right? What I think I will do is use a scrap piece of sheet rock I have (from cutting a new attic access hole), cut it so I can put it around the flue on the attic side and seal around it in the attic. Guess I won't worry about the ugly ceiling for now. I mainly want to seal up the huge air draft the hole is creating.

And what's worse, I am going to have to cut the hole even larger so that the pipe is going straight up so it won't need duct tape around it. The guy must have been drunk as a skunk when he did that work. The attic pipe leans to the left to go through the hole, the pipe from the water heater leans to the left too to make it to the leaning attic pipe. That's why it looks like it does. If I widen the hole by about 1/2" or 1" at most, it will line up properly.

Last edited by Cubey; 10-21-2011 at 10:09 AM.
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Old 10-21-2011, 03:13 PM   #7
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Double wall gas vent pipe?


Type b vent needs 1" clearance from all combustible material. This includes drywall.
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Old 10-21-2011, 03:23 PM   #8
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Double wall gas vent pipe?


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Type b vent needs 1" clearance from all combustible material. This includes drywall.
Even double wall? How do you make up for the gap then?
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Old 10-21-2011, 05:02 PM   #9
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Double wall gas vent pipe?


They make base pieces that the B vent sits in , it's like a square frame that is all metal and the B goes through it at each penetration it acts as a guide and a spacer with the 1" clearance all the way around. I suggest you remove all the existing pipe and re pipe it using bases and metal tape if need be.
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Old 10-21-2011, 05:17 PM   #10
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Double wall gas vent pipe?


You do need 1" clearance to cut out at least an inch around the pipe and then add one of these storm collars to finish it off.

http://www.hardwareandtools.com/Amer...e-6634257.html

This site also has other sizes if you don't have 6" bvent

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Old 10-21-2011, 06:29 PM   #11
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Double wall gas vent pipe?


Okay, yeah.. that's the flange I mentioned that's on the attic side of the ceiling (you can see it through the hole in the photos). Like I said, the guy who did that work must have been almost too drunk to stand up when he did that work. I guess I will still see about patching around it but leaving clearance around it somehow.

Either that or just cut out that corner of the ceiling and replace it.
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Old 10-22-2011, 06:06 AM   #12
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Double wall gas vent pipe?


No that's not what you need, storm collars have that name because they go on the roof above the flashing.
What you need are fire stop pieces that are square with a round hole in the center for the vent to pass through, this design keeps the vent centered all the way through the house to the roof with the acceptable clearance.
You also need B Vent hanger supports they are like big clamps that go around the pipe and secure it to the wall. Go to Venting pipe.com check it out, there are millions of sites out there. From what I seen in the picture you should start from scratch. Remember it's to late if the install is incorrect.
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Old 10-22-2011, 06:58 AM   #13
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What you need are fire stop pieces that are square with a round hole in the center for the vent to pass through, this design keeps the vent centered all the way through the house to the roof with the acceptable clearance.
It appears to me that is what is already in the attic, the storm collar connection was to link to a site that has many types of fittings and escutcheons to cover up the sloppy cut hole in the ceiling.

I say this as the piece you talk about "fire stop" is flat and the piece in the attic looks to be flat to me

Here a better link for proper installation

http://www.mtlfab.com/media/L041r.pdf
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Old 10-22-2011, 09:59 AM   #14
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Double wall gas vent pipe?


The piece in the attic is NOT flat, it is like this:

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Old 10-22-2011, 11:12 PM   #15
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Double wall gas vent pipe?


I found what's called a "wall thimble" at Lowes in the area with vent pipes for water heaters, but I think I only took half of it. *LOL* I thought they were just two connected together to fit in the shelf box better. I only need one half anyway really. I doubt they'll let me go get the other half for free even if I bring back half of it. I guess I can try.

It will only slightly touch the vent pipe (which is 3" diameter) but provides at least an inch of space around it for the most part, save for maybe 1/10" of metal where the pipe goes through and it has 2 small per-drilled nail holes for mounting it to the ceiling. Looks like a much better solution than storm collars.

What kind of caulking could I use to seal around it where the pipe goes through the wall thimble?

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