Exposed rockwool insulation around flue in decompression enclosure

Hi everyone, thanks in advance for your help.

I've purchased and am having installed a woodburning stove insert. (Bodart and Gonay Optifire 800 Green). It's room sealed with combustion air coming directly from outside. It has 2 convection vents seen in picture at the sides of the main flue, meant to take room air in from front of fireplace, heat it and convect it out those vents at top sides.

It's being installed inside a pretty tall, open space (we've lowered the floor, so the fireplace opening is taller) which will be closed off from the living room with fireproof cement board.



At the top of this space, there is a register plate through which the twin-walled stainless steel chimney flue liner exits. Above the register plate, the old brick chimney has been back-filed with LECA pellets.

The installation instructions of the stove (image quoted below copyright Bodart & Gonay) state that even with the convection vents, the enclosure area around the stove must remain vented to allow for 'decompression' around the stove, so that it doesn't overheat, with 200cm2 intake and exhaust decompression vents on each side (this is in addition to the convection pipes) into the enclosure.



So my question is, given there's about 2m between top of stove and bottom of register plate, is it OK that I've wrapped rockwool insulation around the flue in that space.




I wanted to keep the flue warm while the fire's burning and also I wanted to ensure that when the fire's not on (which to be honest will be most of the time) there's less of an uninsulated stainless steel 'cold radiator' ventilated with the living room.

My concern was that, as you can see in the 3rd picture looking inside the 'decompression space', I've got exposed rockwool inside that space, with air moving across it. Is that a problem? It won't be disturbed, but there will be some air flow.

Cheers,
Michael

I was thinking more about rock wool microfibres in the air...

If those fibers will also be free to ventilate out of the register, you may want to consider losing the rock wool, and wrapping the flue with a foil faced liner insulation wrap.

By saying rockwool, I'm assuming that is a high-temp insulation. I used Roxul in my chase, and left it uncovered. Everything I've read about Roxul says that it is NOT harmful to breath the fibers inadvertantly. Now I wouldn't want them constantly coming out into the living space (I have vents both top and bottom in that chase to help balance the humidity/air out in there with the room, but no force air moving in the chase). So, depending on what brand of insulation you have there, you may be fine. Read about the makeup and contents of the insulation.