Americans are warming to an old-fashioned technology to heat their homes: wood-burning stoves.

Some people are looking for cheap heat. Others prefer wood because it can free them from the energy grid. Wood consumption for home heating has risen steadily over the past decade in the United States, reversing a decline in the 1980s and '90s, according to the Energy Information Administration (EIA). The number of homes using wood as a primary heat source has risen 24 percent since 2006, and is projected to rise another 3 percent this winter.

But just as wood is going mainstream, its growth as a heating source is under threat. Environmental groups point to troublesome airborne particulates created by burning wood. Several groups, including the Environmental Defense Fund, the Natural Resources Defense Council, and Clean Air Watch, sent a letter this month to the Environmental Protection Agency (EPA) asking that federal wood-burning standards, set in 1988, be made more stringent.

"[T]he stuff we've learned about particles since the 1990s is voluminous," says Janice Nolen, assistant vice president of national policy at the American Lung Association in Washington. "We have had thousands of studies since then that are not addressed in the evidence the EPA has on the requirement book because they simply didn't exist."

One of the big drivers behind the move to wood is the cost of other fuels. If this winter returns to more normal cold temperatures, households that rely on natural gas could spend as much as $89 more on heating this winter, a 15 percent jump over last year's mild winter, according to the EIA. Heating oil users could spend 19 percent more.

"You look at oil: Prices are high. You look at gas: Those prices are fluctuating like a roller coaster," says Leslie Wheeler, spokeswoman for the Hearth, Patio & Barbecue Association in Arlington, Va. "Wood has remained pretty constant."

For those with forest access, fuel is virtually free, provided the consumer is willing to take the time to cut, stack, and dry the wood. Americans in 2009 consumed about 0.5 quadrillion British thermal units of wood for home heating, only slightly less than the 0.6 quadrillion Btu of fuel oil consumed.

Of course, much of that is for supplementary heating. The number of US households using wood as a primary source of heat is about 2.6 million, the EIA projects. By contrast, the number of households relying primarily on gas heat is expected to top 58.6 million this winter.

Unlike oil or gas, wood is largely independent of electricity, markets, and government. "You're not shifting the burden onto someone else to drill for natural gas and cause dislocation," wrote Cam Mather, a blogger and publisher who lives off the grid north of Kingston, Ontario, in a 2011 post.

Burning wood may conjure up images of dirty smoke billows, but stoves have evolved. When sustainably harvested, thoroughly dried, and properly burned using EPA-certified equipment, advocates say wood can be a virtually smoke-free, carbon-neutral energy source.

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Still, even the cleanest wood stove emits particulates, which have been linked to health issues. Citing a 2008 EPA report, environmental groups say wood combustion devices are one of the main sources of fine particulate air pollution in the US, contributing more than 17 percent of the annual total.

No energy source is perfect, advocates and skeptics agree. If you are considering switching to wood, it's important to consider your location, schedule, and physical stamina.