Metal Stud Heat Conduction. Potential Subfloor Issue?

[NorEaster603]

I will be making a non combustible wall behind my wood stove. My plan is metal stud framing with cement board and brick veneer. Since none of this is flammable i will have the stove a few inches closer than the distance on the sticker to combustibles (but still leaving space for air circulation etc.) Behind this wall is a masonry chimney. The floor is standard wood framing with 3/4” plywood subfloor. The hearth will be R2.2 so i’m not concerned about area directly under the stove. HOWEVER…what about the plywood directly under the metal studs? There is a 2” air gap around the chimney. But i have to assume if the wall will see temperatures exceeding those safe for combustibles that the studs will equilibrate to that same temperature and conduct heat down to the subfloor potentially causing charring or worse.

What should i do here? Insulation under the bottom metal stud? Replace the subfloor under the hearth with 3/4” of cement board? Or am i overthinking this whole thing and it’ll be fine? Thanks!

 

[zak77]

As long as you have air movement around the metal studs, i think you'll be fine. I have a heat shield attached to wood framing with screws and an air gap. After checking it with an IR gun while the stove is cranking, the temps did not concern me. You can do the same once it's assembled to verify there isnt an issue but i doubt it will be.

 

[NorEaster603]

As long as you have air movement around the metal studs, i think you'll be fine. I have a heat shield attached to wood framing with screws and an air gap. After checking it with an IR gun while the stove is cranking, the temps did not concern me. You can do the same once it's assembled to verify there isnt an issue but i doubt it will be.

I’m not sure i can say there is air movement around the metal studs. It will be completely framed in apart from the 2 inch gap around the chimney inside the wall/floor. This would be open into the basement but the original builder had stuffed fiberglass insulation in the gap which i figured i’d do as well. This would not have a heat shield on stand offs but rather be a completely non combustible wall built over a combustible subfloor.

 

[Oakey]

I did the exact same thing as you are describing with metal studs , I just spaced around it with copper tubing the screws would pass through the spacer, sides bottom and top . Cement board and thin brick . I will try and post pics later when I get home .

 

[Oakey]

I did the exact same thing as you are describing with metal studs , I just spaced around it with copper tubing the screws would pass through the spacer, sides bottom and top . Cement board and thin brick . I will try and post pics later when I get home .

1 inch copper pipe not tubing sorry

 

[begreen]

I will be making a non combustible wall behind my wood stove. My plan is metal stud framing with cement board and brick veneer. Since none of this is flammable i will have the stove a few inches closer than the distance on the sticker to combustibles (but still leaving space for air circulation etc.) Behind this wall is a masonry chimney. The floor is standard wood framing with 3/4” plywood subfloor. The hearth will be R2.2 so i’m not concerned about area directly under the stove. HOWEVER…what about the plywood directly under the metal studs? There is a 2” air gap around the chimney. But i have to assume if the wall will see temperatures exceeding those safe for combustibles that the studs will equilibrate to that same temperature and conduct heat down to the subfloor potentially causing charring or worse.

What should i do here? Insulation under the bottom metal stud? Replace the subfloor under the hearth with 3/4” of cement board? Or am i overthinking this whole thing and it’ll be fine? Thanks!

The distance to combustibles is still in play. In this case it might be whatever is behind the metal studs in the wall. If that is wood studs, plywood, etc. Then that is what the clearance is measured to. This is something to think about. If the goal is to get 3 or 4" closer to the wall then it may not make sense to build a 4-5" thick wall in front of the combustible.

If the hearth is constructed to R=2.2 then that is the final determinant. If this meets or exceeds the stove requirements, then it's fine.

May I suggest posting all the details of the project before proceeding? We may be able to save you some time and materials. Is this for a legacy pre-EPA stove? What is the stove make and model? What is the current wall construction?

 

[NorEaster603]

The distance to combustibles is still in play. In this case it might be whatever is behind the metal studs in the wall. If that is wood studs, plywood, etc. Then that is what the clearance is measured to. This is something to think about. If the goal is to get 3 or 4" closer to the wall then it may not make sense to build a 4-5" thick wall in front of the combustible.

If the hearth is constructed to R=2.2 then that is the final determinant. If this meets or exceeds the stove requirements, then it's fine.

May I suggest posting all the details of the project before proceeding? We may be able to save you some time and materials. Is this for a legacy pre-EPA stove? What is the stove make and model? What is the current wall construction?

The stove is a Nectre N550 (VT Bun Baker). There used to be a brick wall but that was asymmetric and poorly supported. There will be nothing combustible behind this wall i plan to build, only a masonry chimney. The wood framing to the left and right of the chimney in this picture will be replaced with metal. The only combustible thing in this equation will be the subfloor and floor joists, and the rafters. With the hearth there will be no direct path for heat to reach this, but my concern is the temperature the wall itself might reach and the temp in the air space between it and the chimney.

 

[begreen]

Great. Most of these concerns are not warranted as long as the stove's clearance and hearth requirements are met.

With the metal framing alongside the chimney, there will be no combustibles involved. If the stove is centered on the existing masonry then it will be fine with a closer clearance. I will download the manual to take a look, but so far I am not seeing any red flags.

What are the hearth construction details?

Will a stainless liner be installed in the chimney?

 

[NorEaster603]

Great. Most of these concerns are not warranted as long as the stove's clearance and hearth requirements are met.

With the metal framing alongside the chimney, there will be no combustibles involved. If the stove is centered on the existing masonry then it will be fine with a closer clearance. I will download the manual to take a look, but so far I am not seeing any red flags.

What are the hearth construction details?

Will a stainless liner be installed in the chimney?

There is a 6” stainless chimney liner installed. As for clearances, since it is a completely non combustible wall my plan is to have around 7” between the back of the stove and the wall. Because of this i’m assuming the temperature of the wall will be higher than wood can take hence my concern for the subfloor under the metal studs.

 

[NorEaster603]

My plan for the hearth construction is a Micore sandwich. Something like 1/2” cement board, 1/2” Micore, 1/4” cement board, 1/2” Micore, 1/2” cement board, then mortar and thin brick.

I’m open to suggestions or improvements to this.

 

[begreen]

My plan for the hearth construction is a Micore sandwich. Something like 1/2” cement board, 1/2” Micore, 1/4” cement board, 1/2” Micore, 1/2” cement board, then mortar and thin brick.

I’m open to suggestions or improvements to this.

You're on the right path, but 1" micore with 1/2" cement board on top will suffice. If only 1/2" micore is available it's ok to stack them on top of each other. If you want to do your sandwich, you can skip the bottom cement board. Just be sure the top layer is 1/2" cement board for more rigidity.

 

[NorEaster603]

Good to know. I thought an inch of micore might be too squishy but if not that’s definitely more simple