"Top Hat" RMH Build Idea

Still contemplating an RMH design since I missed the boat on building this year. My latest idea is to build the core, likely DSR3 style, into a brick base and top it with a heavy gauge steel box. The box would be flanged around the open bottom with even thicker angle iron, sitting on top of the brick, free to expand and contract on a superwool gasket. The flue would rise from the brick bottom of the heater so no holes in the steel box. Essentially the same design as any RMH that uses a metal drum.

Pros over steel drum:
-Longer life via heavier gauge steel than drum.
-Appearance-  A drum would look horrid in our dining room and stacking bricks around it even worse.
-Ease of build- setting a square box on a square base is simpler than building a brick base to support a round drum.
Con:
- more cost up front.

Pros over all-brick bell:
-Responsiveness- It would look better and allow me to “tune” the mass much more effectively by adding bricks along the sides of the metal box until I have just the right balance of heat release and retention. I want some quick head and ability to easily “tune” because the passive solar porch can change temps rapidly and seasonally.  
- Ease of build- Avoids the double skin and refractory materials necessary in the top of a brick bell.
Con:
-Metal won’t last forever even of a thicker gauge and may warp.

Am I on to something workable here, or would a heavy gauge box warp too badly even well above the batchbox exhaust?
What gauge would be sufficient for the box?

Hi Matt;
After reading your post I "think" I have figured out your plan.
You are hoping to use a metal box as the roof of a DSR3?  Is that correct?

I have not built any of the shoebox stoves myself so I am not sure about them.
If you tried this as a roof on a standard batchbox I predict warping and worse could happen.
I experimented with a sheet of RA330 high heat steel as a roof... it did not last a single burn before warping and lifting a stack of bricks!
I am not sure of temps in the upper box on a DSR design, but I have watched the videos and it looks pretty hot in that area.

I suggest having an insulated or otherwise fireproof roof on the DSR and setting your metal box on top of that.
If that roof gets hot enough, perhaps cut a door in your metal box and use it as an oven.

That looks a lot like the stove that Matt Walker brought to the Wood Stove Decathlon back in 2013. But it was probably a smaller system than the one you are describing.

thomas rubino wrote:Hi Matt;
You are hoping to use a metal box as the roof of a DSR3?  Is that correct?

Negative, it's the roof of the whole bell. The core is far below, pictured as the black rectangle(s). Granted, it's still a goodly amount of heat spewing upwards out of the core. I figured it would be fine just like the classic use of a drum over a standard batch box heat riser but with even more clearance between core exhaust and bell top.

Ok, Matt;
That sounds much better!
It will still get mighty hot but your metal should be within safe operating temperatures.
I suggest using 11 gauge metal (1/8")
Were you going to bolt this down or let it free-float?

thomas rubino wrote:Ok, Matt;
Were you going to bolt this down or let it free-float?

Free floating, corralled by masonry so it can't shift around. Like maybe cut a notch out of a course of bricks to sit over the flange so it's held down in a way that it can still expand a bit.  

I would cut the notch out of the base course of masonry so that the steel "hat" is positively prevented from shifting too much. It might also make the seal a bit better. The bricks you might stack around the hat then would not need to be customized to sit neatly; you could use any bricks anywhere.

I like this idea, but reversed. Steel at the bottom, refractories on top. This way:
-highest temperature at the top would be absorbed by bricks
-refractory on top would much better handle heat than metal
-the colder bottom would radiate faster

But it's only theory, because the expanding metal would crack the bricks on top.