Insulating round Flue pipe

[consciouspnm]

I have a modern designer gas fire with a steel flue pipe then comes out of the back and through the wall to the outside. The fire sits on a plynth about 30cm from the wall. The hole in the wall on the inside is larger than the pipe and I am getting a draught through the cavity.

What can I use to block the gap that can take the heat from the flue pipe?

 

[ChrisR]

Eeeek who installed that!?
How big's the gap? You could pinch some rockwool from your loft insulation perhaps, otherwise it comes in big bags.

 

[consciouspnm]

There is actually a steel disk that fits round the pipe to cover the hole in the inner wall but it's just loose at the moment. I was thinking of using rockwool, as I have a roll for another project. I just wanted to confirm that it would take the heat. I'll then screw the disk to the wall to finish it off.

I was there when I bought the house!