It was crazy hot today - time to be thinking about busting out the shade cloth. But instead I got an education on various heating methods.
Part of my reason for putting up a greenhouse was to extend my growing season. But what to do on nasty cold days?
A Rocket Mass Heater, or RMH for short, can warm a space using less than 15% of the fuel required by traditional wood-burning heaters. Paul Wheaton has a really nice page talking about rocket mass heaters at his permaculture website www.richsoil.com, along with this very nice illustration showing how the stove works:
The heated gas 'rockets' up the combustion chamber, drawing fresh air into the stove around the sticks and pushing air out the exhaust. By weaving the exhaust through piping inside a thermal mass, all the combustibles get a chance to be consumed and the exhaust temperature cools as it transfers heat to the thermal mass. The final exhaust is simply moist air that may be as cool as body temperature. After the fire is extinguished, the heat energy in the thermal mass continues to warm the space for hours, even days.
The basic concept was first described in 1982 by the permaculture folks over at Aprovecho. Their aim was to develop an efficient, low-cost cook stove, which can help billions across the world (millions of whom die each year due to smoke and effects of traditional cook fires). The clean cook stove issue is huge - check out the Global Alliance for Clean Cookstoves.
Getting back to using one of these clean stoves (rocket mass heater) to warm my greenhouse, I would want something I can install for the cool months, with an option to remove it in the summer. So Paul's experiment with a 'portable' stove is right up my alley. And I have several whole months to figure out how I would implement this in my situation.
Here's a longer video showing the Portable Rocket Mass Heater Paul Weaton and crew demonstrated on Earth Day, 2011, up in Missoula, Montana.