Hot-water systems –we’ve made various systems, from ones that heat a big-vented tank of water with a copper coil running through it, to heat exchanger thermosiphon units boosting solar hot water.Cooktop or BBQ – old cast iron BBQ plates can work well, or heavy copper radiator plates to put pots and pans on, or just cook over the stream of hot air.Oven – either a converted conventional oven with the rocket under it, or a purpose built barrel oven from old ‘44 gallon’ (around 200 litre) drums.Here are a few things that can be powered with a rocket stove. And here is where your imagination and inner inventor can run wild: anything you can think to do with very hot air can be done from this point. When combustion is complete, we can extract heat from the stove at the top of the heat riser. The drum style rocket stove is not only functional, it’s beautiful WHAT TO DO WITH ALL THAT HEAT The combustion chamber of the rocket stove is heavily insulated to prevent premature heat loss, and an enormous amount of heat is generated by the efficient combustion process. Having ensured complete combustion, and hence maximum heat generation, only then do we think about using the resultant heat. Conventional wood stoves are sucking heat away from the combustion chamber for cooking, space heating or with ‘wet back’ water heaters, meaning the unit just can’t get hot enough for combustion to be complete, resulting in smoke. We are culturally trained to associate smoke with fire but with rocket stoves, sometimes when there is no smoke, there is still fire! When combustion is complete, what comes out the chimney is pretty much only carbon dioxide, meaning no smoke: smoke means incomplete combustion, unburned fuel, or wasted energy. This lack of oxygen chokes the combustion, leading to cool burns, incomplete combustion and lots of smoke and creosote. In conventional wood stoves the air intake is small, and adjustable to even smaller. It gets really hot, the wood burns beautifully, and you hear the air roaring as it charges through the system. This incoming air flows into the feed tube and across the burning wood – creating the same effect as pointing a big air-blower at your fire. As the fire starts, and the burn tunnel heats up, the rising hot air races up the heat riser, drawing lots of air behind it. Rocket stoves are open where the wood is fed in, allowing lots of oxygen to be drawn into the unit. This distinctive sucking of the flames down into the burn tunnel, and the resultant ‘roar’ is what gives rocket stoves their name. In a rocket stove these compounds are sucked into the insulated and very hot ‘burn tunnel’ of the unit where they combust, releasing even more heat energy to drive the rocket process, unlike a normal fire where they are blown out the chimney. When wood is burned it releases volatile compounds that we recognise as smoke or soot or creosote. The main difference between a normal fireplace or woodstove and a rocket stove is that rocket combustion is close to complete. HOW ROCKET COMBUSTION DIFFERS FROM NORMAL COMBUSTION If you are good at scavenging bits they can cost virtually nothing to build, and when you prune your fruit trees you can get the fuel you need to cook dinner, heat your home, and enjoy a nice hot shower. That’s right – you can build these systems in a day or two, and then watch them turn twigs into heat far more efficiently than most wood stoves, with far less set-up cost.
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