filling gap around water heater exhaust pipe and hole in wall

So our exhaust pipe from our hot water heater goes up from the unit, then turns a 90 degree angle to exit the room through a hole in the drywall of the back wall, to the next room. In the next room it turns a 90 degree angle upwards and exits through the ceiling. The hole in the wall from the room the unit is in, is larger than the exhaust pipe. The previous owner had insulation stuffed around the pipe to clog the gap, and a service man said that may be a fire hazard. I'm looking to completely full this gap without causing a hazard. Please coups someone link me to the proper solution to this problem? Thanks!
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On 07/25/2017 12:14 AM, msartore8 wrote:

type b vent wall thimble
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On Tuesday, July 25, 2017 at 12:14:05 AM UTC-4, msartore8 wrote:

The service man said it *may* be a fire hazard. Before I spent too much time trying to find a "proper solution" I'd determine if it actually is a hazard or not.
Did he say why it *may* be a fire hazard?
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and

the key words you want to google search for are flue combustible wall clearance
the flue can get very hot and if it is too close and not properly shielded from a combustible wall can be a fire hazard.
There are also building codes about this
m
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On Tue, 25 Jul 2017 04:51:49 -0700 (PDT), DerbyDad03

Use rockwool, not fiberglass, and there is NO fire hazard.
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On Tuesday, July 25, 2017 at 10:43:25 AM UTC-4, snipped-for-privacy@snyder.on.ca wrote:

But like Mako said, there are building codes and fire codes and I think he has it right, you need a double wall properly rated pipe when passing through that wall. I would also look pretty ugly and obviously half-assed if you stuffed rock wool around it.
And notice I won't take a cheap shot at you here Clare for another wrong answer either.
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On Tuesday, July 25, 2017 at 11:24:24 AM UTC-4, trader_4 wrote:

And I won't take a shot at anyone either but I'm pretty sure a power vented water heater with a Schedule 40 exhaust pipe doesn't need a double wall pipe or get so hot as to be a fire hazard.
That is why I asked the OP if he knows *why* the service guy said it _may_ be a fire hazard. The OP called him *a* service guy. We don't even know what kind of service guy he was. For all we know, it was a service guy from the cable company. One would think that if he was a certified water heater service guy he wouldn't use the word "may" because he would know if it was a fire hazard or not.
Unless we know what kind of exhaust pipe he has, we really shouldn't be tossing out solutions related to piping or types of insulation. For all we know, the previous owner was trying to block sound or air from passing between the rooms around a PVC pipe.
Lots of conclusions being drawn without enough facts to make them.
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On Tuesday, July 25, 2017 at 8:52:47 PM UTC-4, DerbyDad03 wrote:

I start with what is given and he did say that a serviceman told him that the insulation stuffed around the vent pipe could be a fire hazard, which set the stage for the question. So, I assumed it's a conventional water heater with a hot vent. You're right, if it's a water heater that uses PVC pipe, then it's not a fire hazard. We'll probably never know, because the homemoaners usually are never heard from again.
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