Barry Cozymen

As for insulation, hemp can beat sheep wool and it's also more eco friendly, as sheep's wool is surprisingly an insulator with a very big footprint.

And adding hemp shivs to lime is definitely a good way to enhance it's thermal properties. That's why hemplime is such a great insulator.

Pellet heaters have fans for intake and exhaust of fresh air and fumes. The fans (which we don't have in your usual rocket mass heater) and the complete combustion (which we do have in rmh) are what combine to make an exhaust through a wall possible, reason being the aforementioned wind pressure.

So if you would like this to work for a rmh, you'd have to install a fan.

Also, I would be concerned about the few times when the rmh isn't burning at it's optimal levels and is producing soot. When regular wood burning stoves are exhausted on the side of a house without going up above the roof (which is wrong but is still done now and then, sometimes with horrible consequenses eventually happening) you will see the wall becoming darker and darker over time as the fumes from the exhaust leave residues on the wall.

This will also happen during moments when the stove isn't properly burning, or simply every time we're lighting it anew before things get going properly.

It'll be a lot less buildup than with a regular woodstove of course, but it might be something worth keeping an eye on.

Hi, if your flue is high enough, like in our 3 storied home, and the draw of the flue gets enough pull, a standard flue damper (round disc inside pipe) should be installed after the upward bend. In our home, there's close to 5 meters of horizontal pipe with 4 bends including the upward bend and then there's about 9 or 10 meters straight up and out. In our setup the damper goes in the vertical portion of the flue/chimney, right after the last bend. We've only used it without the mass for now, the mass will be added coming warm season, but having operated like this I would hit myself in the head for not installing a damper honestly. I would say it depends a lot on your specific situation if you need one and place of installment should be put at a convenient location where most of the heat has been extracted for longevity of the damper (it also provides a cleaning port!).

Arguably, if you have a 1 story home and 3 meters of horizontal pipe, it could be considered an absolute waste of good money, and in such a case it would probably have more use for a bypass as has been mentioned, which would be more costly but might be a necessity for cold starts on a windstill morning.