As the fire continues, the heat reaches the surface of the masonry in the thermal bank at roughly an inch an hour. Running an evening fire is very nice,” says Wisner. “You get a burst of heat when the barrel heats up. In a rocket mass heater, you might have a fire for 2 to 4 hours (depending on how cold the thermal mass is, as well as the weather conditions) to heat the thermal battery. The rocket mass heater is a different animal. There is a lot of fuel in unvolumunized gases,” Wisner says. “Aside from the horrendous chimney fire scenario, the other thing that comes into play is all the smoke representing unburned fuel. “If you smolder a fire overnight, then you’re losing a lot of heat from the wood, and potentially creating creosote.”Ĭreosote buildup can cause a serious safety issue and wasted fuel.

Most of the time people either bank the stove to keep it smoldering or they wake up to a cold house. “The real problem comes with overnight heating,” Wisner says. A woodstove heats up, and cools off within hours, requiring more fuel. Rocket mass heaters eliminate the hot and cold cycles that are typical with woodstoves. While most people who heat their own homes are accustomed to wood heat, either with a woodstove or pellet stove, Erica Wisner says, “What we’re doing is no longer considered a woodstove.” Wisner and her husband, Ernie, teach workshops throughout the country, and focus their efforts researching the behavior of fire and improving the design features of rocket mass heaters. It requires a fraction of the fuel - about a quarter of the typical amount used in a season with a woodstove - and burns cleanly. Rocket mass heater or woodstove?īroken down in the simplest form, a rocket mass heater consists of a vertical feed tube, a combustion chamber, a heat riser, and a thermal bank that encloses the exhaust tubes. While it has a larger footprint than the vertically built masonry stoves, the simple design and fairly inexpensive materials of a rocket mass heater make it a task practically any thoughtful do-it-yourselfer can tackle. One of the primary differences is a rocket mass heater has an extended horizontal “bed” that can be utilized as a functional area. Rocket mass heaters are a contemporary adaptation to the long-standing technology of masonry stoves where the goal is to heat a thermal battery that slowly releases its warmth rather than attempting to continually heat the air in the room. The heated thermal mass remains warm for hours, offering an immensely comfortable and practical living space. If you think curling up next to a roaring fire during the cold winter months is pleasant, wait until you grab a book and settle on the warm bed of a rocket mass heater. Part of the appeal of this heating system is that the thermal mass becomes part of the furniture, and it's aesthetically pleasing.

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