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More Evidence that “Clean” Wood Burning Isn’t Clean

wood burning stoves cause air pollutionIn an effort to reduce air pollution from wood burning, government agencies worldwide have used public funds to subsidize supposedly cleaner burning devices, such as EPA certified wood stoves.

Replacing old wood stove technology with newer wood stove technology is often touted as the solution to wood smoke pollution, especially by those who manufacture and sell wood stoves. The results of these interventions has been consistently disappointing, and large wood stove changeout programs in Montana and Canada have not improved air quality as projected. Now, from Australia, comes a study  that again shows the folly of subsidizing purportedly cleaner wood burning. In Perth, a town heavily impacted by wood smoke in Northern Tasmania, approximately 80% of the households were supplied with a commercially available catalytic device for their existing wood heater. The manufacturer of the device states that it reduces particle emissions from individual wood heaters by up to 54% in a laboratory setting.

The study measured fine particle pollution levels in Perth before and after the devices were provided.

The results? No significant changes in ambient PM2.5 concentrations were found. These results reflect, once again, the disconnect between lab results and real world results. They show that introducing new “less polluting” technology in the context of continued wood burning is not an effective way to reduce wood smoke.

What does work? The only interventions that have been shown to consistently reduce wood smoke pollution are those that convert households to other forms of heat that—no surprise—don’t involve burning wood.

Catalytic Wood Stoves Shown to Increase Dioxin Emissions

Hazardous chemical sign that should be attached to a wood stove since they create dioxin.People buy EPA-certified wood stoves with the expectation that they’ll reduce air pollution. Ironically, they may be doing the exact opposite.

A study by Finnish researchers published in the scientific journal Chemosphere found that a wood stove with a catalytic converter emits much higher amounts of highly toxic dioxins and furans than one without a catalytic converter. The study’s authors conclude their article with the warning, “…the usage of platinum and palladium based catalytic converters to reduce emissions from RWC [residential wood combustion] should be critically evaluated before wide-range utilization of the technology.”

Unfortunately, this warning has gone unheeded: While catalytic converters have historically been used in some EPA-certified wood stoves in order to reduce fine particle pollution, the EPA’s new wood stove standards, which are more stringent, are expected to drive more manufacturers to use catalytic technology.

The Finnish study burned birch logs in a wood-fired stove with and without a catalytic converter that used palladium and platinum as catalysts and analyzed dioxin/furan, chlorophenol, and PAH (polycyclic aromatic hydrocarbon) production during combustion.

What they found was shocking: although PAH emissions were 24% lower when the catalytic converter was used, the chlorophenol emissions were 430% higher and the dioxin/furan emissions were a whopping 870% higher.

Dioxins are some of the most toxic chemicals known to science and are a potent carcinogen. In addition to cancer, exposure to dioxins can result in birth defects, immune system impairment and reproductive and developmental problems. Notably, threats to human health occur at extremely low levels of exposure to dioxins.

The study exposes a glaring omission in the EPA standard: while EPA-certified wood stoves are tested and certified for particle pollution emissions, they are not tested for the other highly toxic substances they produce, including formaldehyde, benzene, dioxins, and polycyclic organic matter.

Due to active lobbying by the hearth products industry, government agencies have been using public funds to subsidize sales of EPA-certified wood stoves in an effort to reduce fine particle pollution. Studies about changes in air quality following these wood stove changeouts show that these programs did not improve air quality as expected and do not provide justification for further public funding.

In light of the findings of the Finnish study, an even more sinister picture emerges: wood stove changeouts could be more than just ineffective—they could, in fact, make air pollution far more hazardous.

Wood Burning Causes Climate Change: Incentivizing New Wood Stoves Isn’t the Solution

Wood stoves cause climate changeTucked away on page 102 of a report recently issued by the California Air Resources Board (CARB) is a remarkable statement: By 2030, residential wood burning is projected to be the single largest individual source of black carbon in California.

When it comes to climate change, black carbon can be considered Public Enemy Number Two, with scientists stating that it is “…the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing.”  In the atmosphere, black carbon absorbs solar heat. This not only heats the atmosphere, it also melts the earth’s snowcaps and glaciers when these particles settle on the ground.

Eliminating or reducing wood burning is one of the easiest and most effective ways to curb climate change, but the same report from CARB goes on to say that they are considering incentivizing the replacement of old wood stoves with—wait for it—new wood stoves. Unfortunately, this cognitive dissonance is not unique to CARB. Ontario, Canada recently unveiled a similar program targeting black carbon and other short-lived climate pollutants that allocated $400 million for replacing old wood stoves with “new high-efficiency wood stoves.” Not surprisingly, the Hearth, Patio, and Barbecue Association, a trade group that lobbies on behalf of the wood stove industry for these wood stove changeouts, has hailed the Ontario program as “providing an economic boost

While these wood stove changeout programs are undoubtedly good business for wood stove manufacturers and retailers, there are many reasons why they are a terrible idea for climate change.

First, if these programs instead incentivized the replacement of wood stoves with cleaner heating devices that run on natural gas or electricity, the result would be far greater reductions of black carbon and other short-lived climate pollutants. As a bonus, this would also have other benefits, including lower CO2 emissions, lower particulate emissions, and lower toxics emissions. This would be a win not only in terms of climate change, but also in terms of human health.

Second, the realized SLCP reductions from these so-called “wood to wood” conversions will be far lower than the reductions projected by CARB and others. Although EPA-certified wood stoves are predicted to have lower emissions of particulates, including black carbon, based on their laboratory certification values, it is openly acknowledged by the EPA and even by the wood stove industry that certification values do not correlate well with the in-home performance of wood heaters. In other words, the stoves are much dirtier in the real world than in the lab.

Third, the projected black carbon reductions from wood to wood conversions are based on the improved efficiency of EPA-certified wood stoves (i.e. less wood burned per BTU of heat generated) compared to conventional wood stoves—but this efficiency is unlikely to be realized in actual use, especially in temperate climates such as California. A more efficient EPA-certified wood stove may indeed generate more heat per unit of wood burned, but because wood stoves do not have thermostats, they continue to heat the home even after it has reached a comfortable temperature. When a home becomes too warm, the wood stove will be operated at less efficient settings as the user reduces the combustion air to the device. Even worse, the fire may be allowed to die when the house warms up, only to be restarted at a later time–generating massive start up emissions.

Finally, previous government-funded wood stove changeout programs provide sobering cautionary tales by not delivering the expected benefits. For example, every wood stove in the Libby, Montana area was changed out to EPA-certified wood stoves at a total cost of over $2.5 million. The 28% reduction in particulate pollution, which includes black carbon, was nowhere near the expected 56% reduction, and the contribution of wood smoke to ambient PM2.5 levels had not changed several years later.  And in British Columbia, a total of 6067 old wood stoves were replaced as part of a change-out program. An in-depth evaluation of the program several years later noted, “…there has not yet been a clear reduction in fine particulate matter pollution coming from residential wood stoves in BC.” Had either of these programs been conversions to natural gas or electric heaters, the emissions would have plummeted.

It’s good news that governments are finally acknowledging the role that residential wood burning plays in climate change, and are ready to take action. Unfortunately, promoting more wood burning is not the way to do it.

Why Your Neighbor’s Wood Smoke is Killing You

Wood smoke from wood burning devices is hazardous to healthIn many locations, wood burning is the largest contributor to wintertime particulate pollution (PM2.5). An important new study from scientists at the Harvard School of Public Health demonstrates just how harmful this pollution is to human health.

What they found is alarming. In the study’s sample of 2.4 million people, there were higher death rates in zip codes with higher particulate pollution levels than in those with lower levels. Even small increases in PM2.5 led to higher death rates, with each 10 μg/m3 increase in PM2.5 resulting in a 7.52% increase in mortality. This increase in death rates was seen even in zip codes in which the annual exposures were below EPA standards (the current limit is 35 μg/m3 PM2.5 daily).

The new study used satellite data to determine particle levels and temperatures in every zip code in New England, which is a much larger geographical region than previous studies. It then analyzed the corresponding health data of everyone covered by Medicare ≥65 years old in this area from 2003–2008. The results both confirm and extend previous research that shows a strong relationship between particulate pollution, adverse health effects, and increased mortality.

The findings add weight to charges from the public health community that the EPA standards for particulate pollution are insufficient to protect our health, since the air pollution levels tied to higher death rates were just one-third as high as the current levels mandated by the EPA.

As author Joel Schwartz notes, “This study shows that [current EPA limits are] not enough. We need to go after coal plants that still aren’t using scrubbers to clean their emissions, as well as other sources of particles like traffic and wood smoke.” According to Schwartz, there is no clear threshold below which particle pollution is safe.

Since any increase in PM 2.5 levels result in increased death rates, it means our society must rethink our attitudes toward wood burning. We can no longer afford to regard the smell of wood smoke as something evocative, nostalgic, or natural.

The science is not subject to debate: if someone is burning wood, they are shortening the lives of their neighbors.

Last Chance to Take Action on the Bay Area Wood Burning Regulation

This Friday, May 8th, is the final day to submit public comments on the Bay Area Air Quality Management District’s proposed amendments to the wood burning devices rule. The proposed amendments can be read here.

It’s important that the air district hears from people who are concerned about the hazards of wood smoke pollution—they will certainly be hearing from those who aren’t. If you haven’t already sent in your comments, we urge you to do so before the deadline.

Your comments don’t have to be complicated, and they can simply be emailed to the air district at:


In your comments, we encourage you to mention the following points:

  • You feel that wood smoke pollution is a significant issue for public health and the environment.
  • You are in favor of more stringent regulations to reduce pollution from wood burning devices.
  • You urge the air district to step up it’s enforcement of all wood smoke regulations, especially in regards to those who are burning improperly or burning on days when wood burning is prohibited.
  • You feel there needs to be additional measures to protect people from localized pollution “hotspots” on days when there is no wood burning restriction in place. Local concentrations of particle pollution can be 100 times higher for people living near wood burners than what is measured at the nearest monitoring station.
  • You believe that there should be no incentives offered to encourage people to purchase new wood-burning devices, even if they are EPA-certified.

Thanks for taking the time to stand up for healthy air and a better environment.