Adding fire-resistance for steel wood burning fireplace

[curtis73]

First, this is the fireplace I'm installing. It's a steel wood burning fireplace.

It calls for a 3/4" clearance from the back and sides to any combustibles. For simplicity (and because I like overkill when it comes to preventing fiery death) I will be leaving 1" or maybe 1.25"

My concern is the nature of my combustibles; 100-year-old sweet pine. Anyone who has burned some old demolished wood from a renovation project likely knows how that stuff burns. Hot, fast, and hard to extinguish. I'm sure the engineers who built and tested the fireplace took that into consideration, but I'd like to go one step further.

I was thinking about lining the inside of the framing at the back with 1/4" Hardie backer and it got me thinking... is there a better product for this?

The fireplace is going here. (pics below) This wall was an odd, non-load-bearing wall that used to be an exterior wall (before the addition in the 20s), so it's oddly thick until you remove the drywall, T&G sheathing, asphalt shingles. I cut the wall open to recess the fireplace for two reasons; 1) it will occupy 5" less space in the living room, and 2) it put me in a more favorable position for venting without angling around rafters in the attic. The vertical framing you see is new. The paneling there is ancient... as in maybe from 1900-1910 and only about 1/4"

Would you line that opening with something? Treat the wood with something? Stop whining and install the dang fireplace? What could I use to make me sleep a little better?

First photo is a quick CAD I did of the design I'm going for. Second one shows the hole in the wall where it's going.

 

[user 4883]

I'd definitely line it with something. If your like me, I'm going to stoke that until it's cherry red.
If you could only get your hands on some asbestos/cement board siding panels.

 

[slownsteady]

some kind of cement board seems to make sense. I would leave an air gap behind the cement board also. I only glanced at the website...I imagine the fireplace is double-walled or otherwise designed for the fit it recommends. Have you reached out to the "experts" who sell it? Or better yet, the manufacturer?

 

[curtis73]

I went ahead and installed some cement board. I spaced it out about 3/8"

Fireplace is double walled and calls for a clearance of 3/4" to combustibles at the back and sides. I'm giving it 1" to a non-combustible now.

The "experts" who sell it are experts in sales. I knew I was using them for their pricing, not their expertise. They seem to be the WalMart of fireplaces, but the salesperson I bought from at least had a pretty good level of knowledge about the parts I needed, so there's that. The manufacturer has no direct contact so I reached out to one of their dealers and got some good insight. He wasn't too happy with my choice of boxes. I did get the builder grade inexpensive model, but the next step up was nearly 3 times as expensive and I just can't see paying that much. I don't plan on using this as a heat source, I just want the smell, sound, and look of a real wood fire in my living room and toast the occasional marshmallow with my nephews.

 

[Rusty]

I used cement board for a wood stove. I spaced it out with pieces of copper pipe with screws down the middle of them. Walls never got hot.