Framing Around Fireplace Opening for Gas Insert (see pic)
Attached is a picture of what's left of our wood burning masonry fireplace that we are converting to a gas insert. As you can see, the existing brick facing and raised hearth around the firebox have been removed and the hole in the floor where the hearth was has been patched.
I would like to frame around the masonry firebox opening up to the edge of the firebrick to account for the layer of brick that has been removed so when we get a mantel made it will be proud of the wall face as it was previously... then cover the framed in area with granite or marble.
Question: can I frame around the firebox (up to the existing side opening) with wood 2x4 studs as long as I cover them with fireproof cement board? I was going to use two layers of 1/2" board. Cement board and matching stone will also be installed on the floor.
The current width of the opening is about 36" and the insert inself is about 32" wide.
The installation instructions say the insert must be installed in a masonry fireplace or zero clearance unit. Is my plan OK or do I need to use metal studs in the area adjacent to the firebox opening.