Is it OK to plug gap next to steel liner in chimney with unfazed fiberglass??

[oldmanoldman]

I recently had a new lopi wood stove installed in my old fireplace. For venting, we ran a new stainless steel flex liner from top of the unit up through the top of the chimney.

However, there is an open gap around this 6 inch liner right above the top of the stove. I am afraid I am losing much heat up this opening, and I'd like to plug it up so that it is airtight. However, I am wary of putting any product up against the SS vent, as this gets very hot when the stove is operating. For now I've actually got some aluminum foil there so the warm cannot escape completely unimpeded, and this is making some contact with the SS vent..

As far as I can tell, unfaced fiberglass insulation (class A fire rated) is completely non-combustible and would be a viable way to disallow this warm air to escape up the shaft next to the SS vent. Is this OK to do? If not, is there any other way to plug this hole and ensure I am not losing heat up the chimney at all times?

Thanks so much

 

[stoveliker]

No, fiberglass doesn't withstand the temperatures. It may melt.

Best to use rockwool, (roxul) or ceramic insulation.
AND a metal block off plate below that.
Screw into place and silicone the seams. Rockwool allows air movement, so an air sealing by the plate is useful.

Many threads on here about block off plates.