I have wondered this for some time. I just saw a rocket stove (different than a rocket mass heater, but similar) pic posted in another thread and figured I would ask the question. Do rocket mass heaters actually work or are they a temper mental nightmare? If they do work why are they not common? I do not see them talked about often here, is there a reason? People afraid of the inside the house fire going to burn your house down? Too long to get them to temperature? Not enough firewood consumed? Just looking for input.