Stupid pseudo-rocket questions

Hi,

I'm very fascinated by the RMH videos and am currently watching the Freaky Cheap Heat video. I don't think I'm quite ready to build my own RMH for various reasons, one being space/weight constraints in a small cabin.

I was wondering if there are some principles one could take away from the RMH idea and make a regular box wood stove slightly better? I'm not under the illusion that I could achieve anything near the performance, but could at least some of the heat be stored in a little bit of mass?

Some people put firebricks in their wood stove box to store heat. But could more of that be done? Could I just stack a ton of bricks around/on top of my wood stove to have them soak up the heat? What about the exhaust, traditionally very hot in a wood stove? Could I have some of that waste heat siphon off into bricks? I suppose there would be an issue with the conductivity between the chimney pipe and the bricks..

And, in a traditional wood stove that doesn't burn at 9999°F, would taking heat out of the chimney mess with the air flow/burn dynamics?

Has anybody tried taking a few of the RMH principles and making a regular stove keep heat a little bit longer or be more efficient?

High efficiency of masonry heaters is affected by ability to extract the heat from the exhaust. Even if you put bricks on the cast iron stove, it will not extract more. Of course they will get warm being heated by radiation and conduction of the iron touching them. The iron will be touching internal bricks that already extracted as much heat as they could in the firebox. The heat will just get transferred to the stacked bricks for a illusion of improvement. Without them, the heat would be radiated towards the room. They may change the dynamics of this process, but will not extract more.

I already wrote it in some post, but will re-paste it:

Efficiency of the heater can be expressed by an equation:

Ef (firebox efficiency) * Ea (thermal mass absorption efficiency) * Ee (mass emitting efficiency)

Assuming that you have a perfect firebox with imaginary Ef=1 and Ee is also 1 then all loses are in thermal mass ability to accumulate exhaust heat which is expressed as:
Ea = (Tf - Te) / (Tf - Tr)
Tf = firebox gases temperature
Te = chimney exhaust temperature
Tr = room temperature

When you use values: Tf as 1200 C, Tr as 20 C and Te as 100 C you get 93%, but if you allow gases of, let's say 500 C to escape to the chimney then you get only 59%. That's why mass extracting heat from the exhaust is the key.

I you can not build heavy mass, you can always use light barrel with some bricks/cob to extract exhaust heat. This will help a lot.

I see, that makes sense. So "increased efficiency" is out of the window without extracting from the exhaust. Do you think attempting this on a regular wood stove would ruin the burn dynamics? I assume these stoves are somewhat designed for a certain exhaust heat to create the draft?

Another aspect would just be retaining the heat via some mass, even without improved efficiency. It's a common "wood stove in small cabin" experience that the stove burns way too hot, and people open the window to cool it down. Then the fire goes out and 2h later it's cold again.

Even without improved efficiency, could this unfortunate sequence of events somehow be averaged out by stacking a bunch of mass around the firebox?

To determine if you could add mass to exhaust of the existing wood stove would need some experimenting as each one is different. You would be measuring the exhaust temperature before and after extraction and observe the behavior of the stove.
Stacking bricks will surely change the dynamics of heat radiation. For example, maybe you don't want to have too much heat during the night and it would be accumulated in stacked bricks to be radiated during the day.

Experimenting is the key and good people here will help you with details.