If you walk barefoot onto a paved road on a balmy August night, you might notice the retained heat of the day has charged up the massive concrete with quite a lot of residual energy. Despite the sun having set hours prior, the ground is still quite warm. If you then took a step onto a path, mulched with wood chips, you would loose the sensation of radiant warmth. The wood that makes up the mulch is full of pores and airspace, making it a much lighter and more insulative material with less of an ability to store heat. In our modern structures, a large emphasis is put onto insulation, in fact mandatory R-values are written into almost every code book, yet little attention is paid towards mass. And why? We rate gas furnaces on their ability to heat the air of a space, yet the air is constantly being exchanged with every breath of the occupant as well as every small crack found in the houses wall, roof, and floor structures or the automated HVAC system which is constantly cycling in “fresh air.” A super-insulated home may operate so efficiently it could be heated with a candle, yet as soon as a door is opened and fresh air let in, all the heat is sucked away as quickly as it came. The same is not true, however, for a dense thermal mass.
Rocket stoves are a modern take on an ancient practice of heating up mass. Whether admiring the Korean kang stoves, the Roman thermaebath houses, the German Kachelofen tile stoves, the Russian bell heaters or the Scandinavian Contraflows, there is a vast adoption by various cultures to heat dense thermal mass for long term storage and efficiency. Although there are many ways to produce similar results, there are principles that must be adhered to so that a space is safely heated, avoiding the risks of a structure fire or asphyxiation to the occupant. Complete combustion is paramount to extinguish these fears.
Smoke is unburnt fuel. If a fire is hot enough, all the volatiles will be burnt up and the end result is a smokeless chimney. That said, CO2, water vapor and wood ash are consistent by-products of any wood fire. If the wood is burnt hot enough, there is no fear of clogging a horizontal, maze-like chimney with soot and creosote. For this reason, a well-functioning, clean-combusting appliance should incorporate brick, earth, or stone into the firebox as opposed to metal which tends to glow red hot and radiate heat more quickly than internal temperatures can build. It is this use of material, coupled with some basic knowledge of fresh air requirements, that can lead an aspiring stove builder to an effective design, capable of safely heating mass, be it brick, sand, stone or cob or even water in some slightly more complex instances.
During the course of the Rocket Stove Workshop at this year’s Sustainability Skill Share, we will discuss these aspects of stove design and much more. In addition to the principles that make our wood-fired appliances work, we can match this knowledge with tactile skills such as brick laying, site-mixed mortar recipes, earthen concretes like cob and adobe mixes, and some basic fire science. We can even discuss Rocket Stoves to code so that you can understand the legal parameters you might need to navigate to complete a safe installation in your own structure. We will empower one another with the respectful use of fire. If the practice of a good steward is to waste not, then perhaps we can reclaim a few more BTU’s from our wood burning habit at the same time as cleaning up the air downstream for those that live in our valleys and neighboring communities and giving our butts a pleasant warm surface to greet us after a cold day outside.
Jim Schalles has been studying traditional building techniques since 2012 when he was introduced to roundwood framing, strawbale construction and earthen plasters in central Oregon. Since that time he has devoted his working life to understanding these materials and their applications as he focuses on strawbale construction and fire appliances as the main creature comforts of Great Plains living. He has been a member of the Masonry Heater Association for five years and has been building rocket stoves to code as well as offerings of wood-fired ovens, educational workshops, and other clean combusting appliances. He basis his work out of Omaha, Nebraska, where he is the sole-proprietor of Tallgrass Vernacular, a natural building startup with an emphasis on building with vernacular materials.
The Sustainability Skill Share brings people together to learn practical skills in hands-on classes focused on housing, clothing, and feeding ourselves in a world without fossil fuels. In addition to dozens of classes taking place over two days, we will also have a social aspect: camping, meals, a documentary screening, and perhaps music. This event will happen June 1–2, 2019 in Cooksville, Wisconsin. This will be the pilot year of what we hope will be an annual festival of classes related to sustainability, DIY, hands-on, and individual or community self-sufficiency.