As a part of the apprenticeship at Cal-Earth, my colleagues and I were tasked with researching rocket-mass-heaters, which are highly efficient wood stoves that store heat in an adobe or cob bench. A rocket-mass heater can provide superior warmth for a fraction of the cost of a fireplace and produces considerably less poisonous gases by facilitating the complete combustion of firewood. Before our work, the apprentices of fall 2012, Cal-Earth had built two rocket-mass heaters, one of which was semi-functional and the other was completely unusable. We successfully built Cal-Earth’s first fully functional rocket-mass heater prototype. I recommend buying “Ianto Evans’ Rocket Mass Heaters: Superefficient Woodstoves You Can Build” which has detailed information on building a rocket-mass-heater.