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Old 08-09-2012, 05:00 PM   #1
nwav8tor
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Default B-vent Clearance from Combustibles

The B-vent I'm using for my NG heater garage install requires 1 inch clearance from combustibles. While I knoiw this applies to the hole in the roof (wood sheeting covered with asphalt shingles), does it also apply to the hole in the garage ceiling sheetrock? In other words, is sheetroock considered to be a combustible? I'd like to keep the hole in the sheetrock as small as possible.

Paul
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Old 08-09-2012, 05:39 PM   #2
hydramatic
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Default Re: B-vent Clearance from Combustibles

cover the hole with a metal ceiling fan cap. fancy one`s sell for as much a 100 bucks
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Old 08-09-2012, 06:47 PM   #3
danski0224
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Default Re: B-vent Clearance from Combustibles

The paper facing of the drywall is combustible, so your answer is yes.
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Old 08-09-2012, 07:46 PM   #4
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Default Re: B-vent Clearance from Combustibles

Yeah, I forgot about the paper on the drywall. I already have the trim ring and while it is big enough to cover either size hole, you can be sure it ISN'T one of those fancy $100 ones!!

I cut the "first" hole in the drywall right at the pipe's 4-1/2" diameter so I could wedge the vent in place, plumb it up and mark where it hit the roof so I could position the roof hole in the correct spot. That worked well.

I'm off to enlarge the drywall hole now...

Thanks,
Paul
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Old 08-09-2012, 10:36 PM   #5
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Default Re: B-vent Clearance from Combustibles

If you plan to insulate the attic, you also need to put a box or sleeve around the pipe up to a point just above the insulation. I used a section of 8" tin vent pipe, with b-vent ceiling caps at both ends, one from below the sheetrock, and one on top of the 18" of pipe. You don't want insulation sitting up against the b-vent.

You can just barely make out the sleeve in this pic:


And here it is buried in insulation:

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Last edited by Steevo; 08-09-2012 at 10:39 PM.
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Old 08-09-2012, 11:12 PM   #6
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Default Re: B-vent Clearance from Combustibles

Steevo,

I already have an extra piece of larger single-wall pipe just for that purpose. It'll rest on top of the firestop/support just above the sheetrock and run almost to the roof since my vent is only about 18" out from the side wall/eave. Photos to follow after the install is complete.

Paul
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Old 08-11-2012, 08:21 PM   #7
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Default Re: B-vent Clearance from Combustibles

On my previous garage, I used a "fire break" to penetrate the drywall. While you have it on the ground, you will see it is square with a round hole with tabs that extend to the drywall. The tabs give you the 1 inch clearance. Go to home depot, and buy ductwork that snaps together to screw or rivet to the tabs....

The ductwork will be square... And make it the height above your le el of expected insulation. You can then fashion a cover if you like to prevent over zealous blown in installers from filling that square hole accidentally.

Cut a square hole in the drywall, and secure your firebreak with insulation protector. Then install your b vent through the hole... Hook up the furnace or heater.. Test, and then put in the blown in insulation.

Easy stuff!

R
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Old 08-12-2012, 01:43 AM   #8
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Default Re: B-vent Clearance from Combustibles

Here's my B-vent install in the garage attic. I went with batt insulation in the areas that would've been hard to reach using blown in insulation.




A close- up of the firestop/support and associated framing




The 6" pipe I had was just a bit shy of providing 1" clearance from the insulation (needed 6.5" diameter) so I cut some fiberboard pieces and mounted them to the firestop frame. Now I'll have 2-1/2" clearance...




Almost final product attic view. Just need to secure upper corners of insulation blocker pieces.




Pipe in garage just waiting for elbow and heater to be mated to it...


Last edited by nwav8tor; 08-12-2012 at 01:47 AM.
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Old 08-12-2012, 08:17 AM   #9
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Default Re: B-vent Clearance from Combustibles

Quote:
Originally Posted by Steevo View Post
If you plan to insulate the attic, you also need to put a box or sleeve around the pipe up to a point just above the insulation. I used a section of 8" tin vent pipe, with b-vent ceiling caps at both ends, one from below the sheetrock, and one on top of the 18" of pipe. You don't want insulation sitting up against the b-vent.

You can just barely make out the sleeve in this pic:


And here it is buried in insulation:

Not to hijack this thread - but why didn't you go straight up through the roof above your ceiling penetration? Looks like you could have a saved a bunch on smoke pipe?? There must be a good reason...I'm curious.
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Old 08-12-2012, 10:48 AM   #10
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Default Re: B-vent Clearance from Combustibles

I asked Steevo the same question a while back in a different thread. I believe he wanted the stack to exit the roof closer to the peak due to termination height requirements...

Paul
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Old 08-12-2012, 08:37 PM   #11
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Default Re: B-vent Clearance from Combustibles

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Originally Posted by nwav8tor View Post
I asked Steevo the same question a while back in a different thread. I believe he wanted the stack to exit the roof closer to the peak due to termination height requirements...

Paul
Bingo.
Near the peak, it only has to go above the roof a short ways to be above the peak. I didn't want 24" of pipe sticking out in free air, looking like a fishing cabin.
It is a small price to pay for the nicer appearance.
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Old 08-13-2012, 11:48 AM   #12
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Default Re: B-vent Clearance from Combustibles

They make what's called a thimble for holes through combustibles.

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Old 08-13-2012, 10:57 PM   #13
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Default Re: B-vent Clearance from Combustibles

Isn't that thimble for wall penetrations in horizontal runs, not ceilings and roofs? For my vertical run, I used a combination fire stop and support above the ceiling sheetrock. The sheetrock is only 5/8" thick. I don't think thimbles are made for such small thicknesses...

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Old 08-13-2012, 11:19 PM   #14
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Default Re: B-vent Clearance from Combustibles

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Originally Posted by Steevo View Post
Bingo.
Near the peak, it only has to go above the roof a short ways to be above the peak. I didn't want 24" of pipe sticking out in free air, looking like a fishing cabin.
It is a small price to pay for the nicer appearance.
not so, to qualify for a fishing cabin it also needs to be leaning on about a 30 deg angle.........lol
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Old 08-13-2012, 11:22 PM   #15
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Default Re: B-vent Clearance from Combustibles

nice job
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Old 08-14-2012, 12:40 PM   #16
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Default Re: B-vent Clearance from Combustibles

No, the thimbles aren't just for wall penetrations. Think about insulation in a ceiling or a garage with an attic space that has a floor.
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Old 08-14-2012, 11:24 PM   #17
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Default Re: B-vent Clearance from Combustibles

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... Think about insulation in a ceiling or a garage with an attic space that has a floor.
I hadn't thought of that situation, but I'm thinking about it now

I could see where a thimble would be ideal for such an install...

Paul
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Old 08-14-2012, 11:27 PM   #18
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Default Re: B-vent Clearance from Combustibles

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nice job
Thanks. One square filled, now just gas, electric, lighting, insulation, final mudding, painting and floor epoxy to go,,,

Paul
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