Does this application still require a 1" clearance from combustibles?
If that’s sheetrock, then it isn’t “combustible” and there is no issue. Isn’t sheetrock used to provide a fire barrier between the garage and home?
However, if that is a garage, then there is void in the fire barrier. The gap should be protected by a flange to prevent flame entry into the structure above the ceiling.
B Vent manufacturers will disagree and tell that a 1" clearance is required.
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I think the difference is due to the different purposes. One is with performance under the conditions during a fire (where it is considered noncombustible), and another is with performance during exposure to a constant high-heat source (where it is considered combustible).
Correct?
I believe it is “combustible” as it will burn.
It is “fire-resistant”, not “fire-proof”
Decent article…
Once again, it has nothing to do with drywall manufacturer, it has to due with what the Manufacturer recommends for the installation of their product. And how the product was tested by whatever agency validates the safety performance of the rpoduct(UL). 
The dryall manufacturer can say whatever they want about their product…
They do no make B Vent.
Pyrolysis is also taken into consideration…
Anyone know of a single problem caused in not having clearance?
Many fires in the north from pipes too close to combustibles. Watch the news this heating season or check with your fire department if need be for verification.
Brian,
Don’t you have to have an absence of oxygen to be called pyrolysis?
No, I haven’t seen or heard of a problem with a smaller that 1’’ clearance but
still call it out.
Pyrolysis is the chemical decomposition of organic substances by heating
Thanks, but did they blame the drywall clearance?.
Here is a picture of drywall in an interior utility closet that didn’t ‘burn’ under pretty much worst case scenario with a flue! I ran into this a few years ago. I think someone made a boo boo when they were re-roofing.
Think I need to get a propane torch and see what happens , though I seem to recall a discussion here in the past about materials becoming more flammable over time when exposed to heat .
Read all of this and pay particular attention to the last paragraph. Provided Larry’s information is correct, drywall is considered non-combustible by 3 national model building codes, I don’t care what the b-vent manufacturer’s say about it.
Remember to pay attention to whether there is wood behind the drywall within these clearance distance situations…
The paper is the combustible it says.
Did you read it ALL Bob? The part that says “drywall is considered non-combustible by 3 national model building codes”
Take a piece of drywall paper and see if it lights up right now then tell us what happened.
Seriously i read that it is the paper that is flammable and one of the other sites on this thread talks about type x drywall so apparently it is not a good idea to have that stuff in direct contact.
It did not say it was “flammable”. It said it was in a category called “limited combustible” and is treated as non-combustible by 3 model building codes.
Someone post a picture of sheetrock with scorch marks on it from any type of vent and I’ll change my view.
I looked at various threads on other boards including the ICC and their are different opinions.
The major opinion, appears to be that it is being enforced at 1 inch in new construction