Okay, so, after watching the video of him explaining the "bell" feature...my mind keeps going back to the toxic gases. With a flue pipe system like in the RMH, surrounded by huge amounts of cob, I would feel safe, and not consider any chance of leaks happening (barring massive cracking). But with this bell system, am I wrong in understanding that it's a big empty chamber, and you might have 34-4 inches of stone, masonry, etc? Because if so, I would constantly be worried about a leak between the bricks, or even the fact that masonry is much more porous than a flue pipe would be? Also, even without an actual leak, due to the porous nature of masonry, what's to keep the toxic fumes from soaking into the masonry and building up? In addition, just addressing the nature of the battery...doesn't less mass due to the chamber being empty mean less storage of heat?
These concerns may have already been addressed, or be kind of silly, as I'm not educated on how the carbon monoxide problem works, so I appreciate any guidance.