On cold, still winter nights in San Francisco, it's illegal to use a fireplace. As in a handful of other places, the local air quality agency recognizes that the pollution from burning wood is a health threat—the tiny particles found in soot can lodge in someone's lungs, cause asthma attacks, and increase the risk of heart disease. By November, new homes in the area won't even be allowed to include more efficient wood stoves.
But would an ultra-efficient new wood stove—one that produces virtually no soot—make sense in other parts of the country, where wood is still commonly used as a source of heat? A startup with a smart stove, powered by electronics, thinks that helping homeowners switch to its product could dramatically lower pollution.
"A lot of the wood stoves that are already out there are very inefficient, so they waste heat, they waste money, and they're also very dirty," says Taylor Myers, a graduate student at the University of Maryland and co-founder of MF Fire, the startup making a new wood stove called the Mulciber. "Our biggest concern is the health problems that come with them being dirty."
A typical fireplace or wood stove sucks in air as smoke goes out the chimney, and it's an inexact, unpredictable process. "These wood stoves don't have a whole lot of control over how much air gets into the fire," he says. "It turns out that being able to control that air is really important if you want the wood stove to burn clean."
The Mulciber uses a fan to drive air throughout the system, forcing the fire to burn as completely—and cleanly—as possible. A smart controller inside the stove measures heat and continually adjusts the fan so its fire keeps burning exactly as it's supposed to. The electronics also make the stove easier to use.
"It's much easier to get the fire started, it's much easier to keep the fire going, and it will ultimately be a much easier experience for the user across the board," Myers says. "Less cleaning, less work."
Right now, about 2.5 million households use wood as their main source of heat in the U.S., and another 9 million use it as a secondary source. And in some places—like the Northeast—the use of wood has been quickly increasing.
That's not necessarily a bad thing. Depending on how you calculate the carbon footprint, wood is better for the climate than a heater running on gas or coal-powered electricity. Unlike fossil fuels that are dug up from underground, wood is already part of the natural carbon cycle; if someone's using wood that fell naturally in their background, or that they would have cut otherwise anyway, the wood would have eventually released carbon. As the tree grew, it took in carbon itself.
But a typical wood stove is also a huge source of black carbon, or soot, and that's what causes health problems. An older wood stove might emit as much as 40 grams an hour of particulate matter. New U.S. EPA rules say that anything on the market has to emit no more than 4.5 grams an hour (effectively making almost everything that was on the market illegal). The Mulciber stove emits only 0.2 grams an hour, less than half of the smoke from a cigarette. If you walked by a house using one of the new stoves, you might see a tiny puff of smoke when the stove started. But you'd probably see nothing at all, because there's basically nothing coming out.
"What our stove does differently is it doesn't make very much of that particulate matter at all, which makes these clean, so the people who do use wood stoves can continue to use them without polluting the air," says Myers.
The stoves are currently in beta-testing, and the startup plans to start selling them later this year.