Cedric Scott

I am based in Ireland, quite near sea level where the winters are rarely cold enough for snow.

I do like the sound of a smaller footprint bell, though the designs I have seen are all front loading rather than J-tube, and usually have a metal "p-tube" to deliver secondary air - is this the design you are talking about? Or is there a simpler design? As simple as possible would be ideal - this isn't a big space, after all.

I would love to do a simple design like this, but I am much less familiar with the bell concept than the traditional rmh.

Can I simply build a standard J-tube with heat riser, but replace the barrel with a brick mass to form the "bell," and have the chimney exhaust from the base of the bell so that the coolest gases leave from the base of the chamber?

If anyone has reference to any guides or examples, that would be amazing!

I've been researching rocket mass heaters for some time and had a few questions for those with considerably more experience than me!

My plan is to build a RMH sunken into an earthen floor, with only the barrel of the heat riser and the feed tube opening visible, and to have the floor act as the thermal mass.
This is mainly due to space considerations (the structure will be 12 x 8 feet), so a huge thermal mass bench may not be the best option here.
Anyone out there with RMH's in a small space like this - would it be too much heat for such a small insulated room? Is there a better alternative?

Can the metal duct typically used within the thermal mass be replaced with a brick tunnel sealed with cob? This would be under an earthen floor so I am worried about the strength of the ducting. The metal ducting seems to be quite expensive in my area, maybe I am looking for the wrong material.

What sort of protection would a wooden wall need, near to the barrel?
Should the burn tunnel be insulated with perlite/ceramic insulation despite being submerged in an earthen floor?

This is all relatively new to me so any help at all would be really appreciated!