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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>In Aprovecho’s very well written paper “Design Principles for Wood Burning Cook Stoves” they recommend against high mass stoves such as the Lorena stoves they had worked with many years back.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It is obvious to me why you would want an insulated stove to avoid loss of heat from the fire to the outside as opposed to the pot. But I am very puzzled as to why a sheet metal stove would be better than a heavy clay one. It seems to me that heat from the fire will be transmitted much more quickly through the thin walls of a metal stove (without thermal insulation such as ceramic fiber) than through a massive earth wall. To orient myself I checked the thermal conductance of a few materials in Watts/meter/degree Kelvin. Insulating materials such as ceramic fiber are about .03-.04, insulating brick .15, dry earth 1.5, stainless steel 16, and carbon steel 43. Compared to steel the earth is a good insulator. An interesting aside, dry sand is similar to insulating brick at .15.<o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>The fact that the high mass stove stores the heat in the stove body rather than immediately transferring to the outside air as a metal stove would do wouldn’t seem to change the heat lost from the fire.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Huck<o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-family:"Arial","sans-serif";color:#400040'>Huck Rorick</span><span style='font-family:"Times New Roman","serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Arial","sans-serif";color:gray'>Executive Director<br>Groundwork Institute<br>2640 Silvercrest Street<br>Pinole, CA 94564<br>Phone: 510-222-4111<br>email: </span><a href="mailto:huckrorick@groundwork.org"><span style='font-family:"Arial","sans-serif";color:blue'>huckrorick@groundwork.org</span></a><span style='font-family:"Times New Roman","serif";color:gray'><br></span><span style='font-family:"Arial","sans-serif";color:gray'>Website: </span><u><span style='font-family:"Arial","sans-serif";color:blue'><a href="http://www.groundwork.org"><span style='color:blue'>www.groundwork.org</span></a></span></u><span style='font-family:"Arial","sans-serif"'> </span><span style='font-size:11.0pt'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p></div></body></html>