On a cool, gray Saturday, the tent hosting the first wood-stove decathlon on the National Mall looked something like a Native American longhouse, but covered in vinyl and with a dozen metal chimneys poking out. From the outside, those metal stacks emitted no smoke, which made it a surprise to encounter a wall of heat upon walking into the tent.
All of the 14 stoves inside — equipped with the latest in oxygen sensing technology, catalytic converters, and remote controls — were burning there in the face of this fact: Some 400,000 years after the discovery of fire and the first human stoves, we're still trying to perfect the technology.
"It is seen as a hillbilly energy; it's not seen as a future energy," says John Ackerly, the founder and president of the Alliance for Green Heat, the event's main sponsor. With this event, on the heavily trafficked National Mall, he'd like to change that.
Over the course of the five-day decathlon, the 14 units will be tested for emissions output and fuel efficiency. The $25,000 prize — and, conceivably, the title of "most advanced home stove in human history" — will go to the team that has the best combination of scores.
The Promise of Wood Heat
"Wood can be very dirty," Tom Butcher, a contest judge and combustion researcher with Brookhaven National Lab, tells me. It's far more polluting than gas or oil if burnt in an open pit (as half the world's population does). And it's not just emitting the usual problem pollutants — such as carbon monoxide and carbon dioxide — but also acrid chemicals such as benzene and formaldehyde. In the developing world, the World Health Organization estimates, 2 million people die prematurely due to indoor use of wood fire.
That's because in that dirty — though delicious-smelling — smoke from the open pit, there still are compounds that could be further broken down. For fire to burn clean, it has to burn completely. In some designs, that means burning hotter. But then the fuel gets spent too quickly. Reaching the optimal balance of emissions reductions and efficiency is a delicate balance — and the central challenge of the decathlon.
"Some people like to say, 'This is not rocket science — it is a lot harder,' " says Butcher.
There are two main ways to burn wood completely, he explained. One is gasification.That's when the wood is heated to a point where it breaks down to a gas. Then, that gas is burned. (It's actually a 19th-century technology that was used to power some early cars — and a few current gonzo ones.) Another strategy is to employ a second combustion chamber in which the smoke from the first burns and passes through a catalyst to be more easily ignited for a second time.
The contest has also inspired some out-of-the-box thinking.
A few months ago, Taylor Myers and his team at the University of Maryland didn't know the first thing about wood stoves, but decided to take on the challenge anyway. At least on Monday, their stove, Mulciber — named after the Roman fire god — was leading the rankings in terms of emissions.
What had set their contraption apart from other models was a novel idea: forcing air into the stove. Usually a stove draws in air via natural convection. The Maryland team's device injects air to fully combust the fuel. "We didn't come in with any of the preconceived notions," Myers, a graduate student, says of their success. "I think we're on the verge of making something really great that can completely change how people can use wood energy."
But Is Wood Heat Practical?
However innovative the engineering, a true wood-heating revolution seems doubtful. Interest in biomass fuel peaks up when costs of more conventional fuels are high, but the current natural-gas boom is likely to keep gas in the status quo. And wood's chief advocates will admit there's a hill to climb in terms of emissions. "It's never going to be as clean as gas," Ackerly says. "But we're a renewable."
It's long been an intoxicating environmental idea to create technologies that help individual homes work off the grid. But promise doesn't always immediately translate into practice — just think about the prevalence of solar panels.
But in places where wood is abundant and cheap (perhaps even free), wood heat can make sense. Twenty percent of homes in New England have some form of wood-fired heat, the U.S. Energy Information Administration reports. And, overall, "the use of cord wood and wood pellets as the primary residential space heating fuel has increased by 39 percent since 2004, to about 2.5 million households in 2012." Add to that 8 percent of houses that use wood as a secondary source of heat.
"Wood is attractive for a lot of reasons," Butcher says. But "we have to get the emissions down from wood-burning in order to achieve cleaner air."
There's a huge difference between the environmental impact of a clean wood burner and a dirty one — and the Environmental Protection Agency has been regulating them only since 1988. "Seventy percent of stoves in America were built before the EPA started regulated them," Ackerly says. Because wood is so variable (the type, moisture content, etc.) EPA has the units tested over two weeks at different burn temperatures. "The cost, including safety [testing], is $30,000, $40,000, $50,000," Steve Rhodes of HWAM, one of the decathlon contenders, says. His model, currently available in Europe, is set by a computer thermostat, and its automation makes it difficult for EPA to test at different burn rates. The agency is currently working on updating its stove regulations, making the emissions limits more stringent.
Walking among the stoves, there's a level of artistry and craftsmanship that just doesn't go into your typical home gas or oil burner. There are elegant stacked bricks, sharp industrial lines, old-timey enameled fireboxes, and one model with giant metal moose antlers. These are meant to be seen, not hidden in the basement. There's a "gather round" design element common to all of them. Which is necessary, because the stoves require some work, in loading the wood and keeping the fire going.
"People like to come and just watch the flames; for us it's a selling feature — it has a beautiful flame," says Niels Wittus, a contender with an elegant gasifier stove. "A lot of people today don't know that you can have — and this is not only ours — but the stoves here burn without any smoke essentially, and that's a good thing."