Substitute white non-combustible board above 6000cl unit with cement board?

[Retrojoe]

I am getting ready to add the El Dorado Stone veneer to the wall surround around my gas fireplace. I had the 6000 CL installed and then used Perma base cement board around the entire wall framing which is flush with the white non-combustible board attached to the unit. I was trying to do some research and one of the dealers told me that the manufacturer used a Micore 300 board. I'm wondering whether this will accept mortar and the weight of the stone veneer? Also, from some of the data sheets I've read, it says that the board should not exceed exposure to more than 85° f. This is confusing because the installation manual for the unit mentions that the temperature above the unit can reach 200° f. Would it be a bad idea to detach that board and substitute it with Durock 1/2" cement board? I'm at least confident that it will hold the weight of the stone and mortar but just can't find anything about this whiteboard doing the same.

I've also been reading a lot of the posts on here about what is acceptable to use on the hearth. I have a raised heart and used the Perma base which I do believe has some of those little white beads in it. There will be one and a half inch thick hearthstone on top of this. Is this a concern with gas fireplaces or just wood burning where the flame is actually exposed to the exterior? I would appreciate any experienced installers to give me some input on this. Photo attached below.

 

[Lennox65]

I am getting ready to add the El Dorado Stone veneer to the wall surround around my gas fireplace. I had the 6000 CL installed and then used Perma base cement board around the entire wall framing which is flush with the white non-combustible board attached to the unit. I was trying to do some research and one of the dealers told me that the manufacturer used a Micore 300 board. I'm wondering whether this will accept mortar and the weight of the stone veneer? Also, from some of the data sheets I've read, it says that the board should not exceed exposure to more than 85° f. This is confusing because the installation manual for the unit mentions that the temperature above the unit can reach 200° f. Would it be a bad idea to detach that board and substitute it with Durock 1/2" cement board? I'm at least confident that it will hold the weight of the stone and mortar but just can't find anything about this whiteboard doing the same.

I've also been reading a lot of the posts on here about what is acceptable to use on the hearth. I have a raised heart and used the Perma base which I do believe has some of those little white beads in it. There will be one and a half inch thick hearthstone on top of this. Is this a concern with gas fireplaces or just wood burning where the flame is actually exposed to the exterior? I would appreciate any experienced installers to give me some input on this. Photo attached below.

View attachment 307681

If you look in your install manual you will see that there is no requirement for additional hearth extension or non combustible material directly in front of that model fireplace.
As for the Micore board at the top of the fireplace, unless the manual says that you can substitute Durock, I would not do it.