Rocket mass heaters are the epitome of KISS (Keep It Simple Stupid). They work on the concept of heat rising. Basically, a fire is built with a column on one side for heat to rise into and a suction hole is left for fresh air to be sucked into via the draft created by the rising heat. The resultant fire is extremely efficient and is as close to complete combustion as I have ever seen in a wood-burning application. Once the fire is going in a rocket mass heater, the fire leaves almost no ash and produces almost no smoke (various polyaromatic hydrocarbons for the chemistry nerds out there). You’re left with almost all water vapor and carbon oxides. Below are 2 videos of pretty significant rocket mass heaters being built/used. Both are from Paul Wheaton, a permaculture evangelist, who runs permies.com, a great resource for any permaculture questions.
Paul Wheaton from permies.com demonstrates multiple variations on the rocket mass heater.
Paul Wheaton videos while Ernie & Erica from permies.com build a rocket mass heater into a raised bed that will be covered by a greenhouse.
The system still works, though less efficiently, with a short column above the flame. The loss in efficiency is balanced by the increased portability of some rocket stoves. This technology was developed heavily by Ianto Evans, who was looking for a way to improve the lives of those who use wood-fired stoves as their livelihood. While creating a cob bench and decking out a house is not everyone’s cup of tea, keeping greenhouses warm overnight or having an easy to carry but highly effective camp stove broadens the horizon of those who might be interested. Check out some of the many other YouTube videos posted with the tags “rocket stove” or “rocket mass heater”. There are some pretty cool variations out there. If you’re interested, Evans’ book is available via Amazon at the link below: