Glenn Herbert

Adding mass to a Liberator would be as simple as building a hollow brick box beside/behind the stove and routing the exhaust through it, in one side and out the other side low, and no straight-line airflow so the air has a chance to eddy and give up heat to the brick. It could be as small as a 20" square box a couple-few feet high. I would suggest making it on the short side, with a temporary sealed concrete paver top, and if the exhaust to the chimney is still hotter than you want, add a couple more courses of brick to absorb more heat.

You can make a rocket mass heater entirely from cob. I once built a rocket cookstove with enclosed chimney suitable for venting outdoors, and that design could easily be modified to include some heated mass around the core without taking up much more space.

I would use standard fiberglass rope made for stove door sealing, with furnace cement as needed to mount it to the frame.

I think a seal as you describe would work as long as the metal edge was sunk deep enough into the sand. Not sure how much is necessary.

I don't think the top is the best location for a radiant panel, though; it would be sending heat up to the ceiling, not out into the space where people could quickly feel it. I would set an access panel into a face of the bell, to serve two purposes: instant heat directly to the room occupants, and easy access for inspection, maintenance and repair of the combustion core without having to dismantle brickwork. A steel angle frame anchored to the masonry, with a flat steel panel screwed into it, works excellently in my experience.

I built my bell from old red clay bricks laid up on their sides, covered by an outer skin of cob (about 6"/15cm). I did use firebrick for the top third and ceiling; red clay brick may not last as long, but if given generous clearances to the riser top should be good for many years.

6" is the upper limit of cob thickness I would recommend, as that takes several hours for the heat to start coming through and heating the room. 4"/10cm would probably be the best balance for mass and heat transmission considerations.

I understand batch box firings generally last around an hour, so if a "standard" daily output is based on two firings, multiplying daily yield by 12 for continuous firing would make sense. I would probably cut that in half for uncertainty in actual length of a firing plus the unlikelihood of actually getting 24 hours of continuous burning. You might need a considerably larger bell/mass to properly absorb all that heat; the hotter the mass gets, the less of the combustion gas heat it will be able to absorb.

Very nice demo and explanation. I want a tenon cutter! I have done it with a jury rig on my table saw, but for a common tenon size, the one shown would be the bomb.

I would multiply the BTU/hr by 24 to get BTU/day, then convert that to KW/day or whatever units are appropriate.

I have built wood-fired pottery kilns entirely from cob which reach up to 2000 F for several hours continuously. The clay at the hottest points does shrink, crack and distort, but holds together for years. These points are surrounded by 2000+ F temperatures and variable atmosphere for hours on end. An arched/domed cob ceiling of good native clay with a separate cover layer of cob would probably be durable, as it would be subjected to much less intense conditions. Of course, clays vary, so you would want to test your clay for heat resistance and stability.

Since a flat barrel lid a few inches above the riser top has proven to be durable, I think a half-barrel bell top at least 6" above the riser should work too. A foot of clearance would be even safer. It might be beneficial to add a sheetmetal spacer an inch above the barrel at and around the riser location to allow the barrel to radiate heat away from the hottest area.

I would definitely install an access/inspection port that would allow you to look at the bell top in this case, until it is proven that such a system is durable.