MattB4: A rocket stove is NOT the same thing as a rocket mass heater. The mass heater is storing heat that otherwise would have been vented to the great outdoors. The stored heat is slowly released into the room, long after the fire has gone out. A basic wood burning stove is not capable of releasing heat for hours after the fire has burned out.
As an example, I want something to warm my feet, so I light a candle and set it next to my feet for a couple of hours. When I blow out the candle, the heat ceases. Now, if I go a different route with the candle, I can have heat a bit longer after I blow out the candle. By covering the candle with 2 clay flower pots, the pots heat up and create thermal mass and radiate the heat from the candle. When I extinguish the flame, the flower pots are still radiating heat for quite some time after the flame is gone. This is what the rocket mass heater does. It stores the heat that would have gone out through the flue.
It is the same way with the rocket mass heater or any mass heater. Why would anyone let 100's of degrees of heat escape via the flue, if they could contain that heat in some kind of mass that would slowly radiate into the home?
Please don't confuse the twig burning of a rocket stove with the amount of kindling that is used in a rocket mass heater. Earlier, you mentioned something about a wood stove using 80 lbs of wood per day, while a mass heater used 60 lbs per day. I like the idea of saving 20 lbs per day; over the course of 5 months, it is a considerable amount (3,000 lbs).
If burning a fire for two hours will generate enough thermal mass heat to radiate into the home for several hours, then the savings are probably more than the 20% you have mentioned. I am inclined to believe that a 2-3 hour burn in the morning and a 2-3 hour burn in the evening, would be adequate to heat 1000 sqft. With my wood burner, I had to burn wood all day long. That's 18 hours compared to 6 hours with the mass heater.
The woman in the earlier posted video, who lives in the NE, states that she has to heat for 6 months. She is adamant that the amount of wood used is greatly reduced since she started using the rocket mass heater. She has no reason to lie. The amount of ash that she cleaned out of her heater, over a 3 month period of time, is about what I would clean out after a month of using my wood burner.
I used to laugh at straw bale homes, until 2 of my aunts constructed 2 straw bale homes. Neither of them have used their heat this year. They usually kick on the heat in January to bring the inside temp up 10 degrees. Straw bale homes are capable of maintaining a constant temp. Our nights have been in the mid 20's this week. I'm one of those people who have to experience something in order to believe it. People wouldn't be using mass heaters if they didn't perform well.