How to seal a B vent

[nighthaw2k]

The instructions for my heater state to fill the cavity around the B vent with 350 degree Silastic. Were do you find this stuff. I found some 3M fire rated type caulk but no Silastic. Can anyone help me with this.

 

[Jackfre]

If I may ask, what make and model heater is this. Is this a wall thimble application?

 

[HVAC Phil]

The instructions for my heater state to fill the cavity around the B vent with 350 degree Silastic. Were do you find this stuff. I found some 3M fire rated type caulk but no Silastic. Can anyone help me with this.

I use high temperature caulk(red stuff). I think it's rated to 550, which the outer shell of b-vent never gets.

 

[nighthaw2k]

Its a Mr Heater Big Maxx 75000 btu. Yes i'm running a thimble. I did buy some 3m red type sealant. I also picked up some duct work sealant from Home Depot.