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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.

Wood smoke pollutionThe EPA’s Rules for New Residential Wood Stoves: A Sell-Out to the Wood Stove Industry?

On February 4, the EPA issued its long-awaited final rules for the manufacture and sale of new residential wood stoves. We weren’t fans of the proposed rule, and we think the final rule is even worse. After intense lobbying, the EPA caved to industry pressure, and the result is a rule that may do more harm than good to air quality.

Cordwood Testing: Up in Smoke

One of the biggest problems with the existing EPA wood stove certification process is that it uses kiln-dried lumber arranged in a crib formation. Since people don’t operate their wood stoves like this in the real world, the proposed EPA rule sought to address this by specifying the use of cordwood in the testing process.

Unfortunately, lobbying from the wood stove industry spurred the EPA to back away from this common sense step forward and to revert to testing with kiln-dried cribwood, not cordwood, for stove certification. This makes it impossible to extend the in-lab findings to the real world. Even in laboratory tests in controlled conditions, emissions from burning cordwood are higher than from burning cribwood (see studies here, here, and here), so in-home emissions will certainly be higher than projected.

Lower Wood Stove Emissions—But For How Long?

The EPA’s decision to lower allowed emissions from wood stoves in the new rules was applauded by health and environmental groups as a way to lower particulate matter (PM) emissions. But a closer look shows that this limit may have no effect—or even the opposite effect—on emissions in the longer term.

To meet these lowered emission limits, wood stove manufacturers are likely to use catalytic wood stove technology. Unfortunately, these catalytic components can break down in as little as two years. And when the components begin to wear out, the PM emissions increase dramatically. Stove maintenance is entirely voluntary; the proposed rule does not address the issues of degradation or proper maintenance of catalytic components.

Clearly there’s no economic incentive for the user of the stove to replace the catalytic components. There is also no functional reason for them to replace the catalytic components: the negative consequences of degraded catalytic components, which are primarily increased emissions, occur mostly outside the end user’s home. Thus, there is no reason to think that owners will replace the degraded catalytic components or expend the effort to maintain them properly.

The EPA states that the lifespan of a wood heater is over 20 years. Therefore, after a few years of use, wood smoke emissions from catalytic wood stoves will potentially be as high as those from an uncertified conventional wood heater. Thus, the unintended consequence of the EPA’s lower emissions limit is likely to be higher emissions.

The Long Phase-Out Period

After lobbying from the wood stove industry, the EPA settled on a generous (to industry) 5-year phase-out period for manufacturers to transition to the new standards and sell off their existing models.

The industry is already leveraging this extended transition as a way to gin up sales of wood stoves by making consumers feel like they must act now before the new EPA rules take effect (and prices increase). One ad for an outdoor wood boiler urges consumers to act now, claiming that they will only be available for a limited time:

Outdoor Wood Boiler Ad

VOCs and Air Toxics

In their summary of the final rules, the EPA claims that the lower emission limits will reduce VOC pollution. Unfortunately, as far as we’re aware, there is no scientific basis for this claim.

The new rules do not test for, or necessarily reduce, VOCs or air toxics (including formaldehyde, benzene, dioxins, and polycyclic organic matter). Importantly, studies show that these are not reduced in parallel with PM emissions (see here, here, and here). One technical report prepared for the EPA concluded, “The data demonstrate that particulate emissions cannot be used as a surrogate measurement for POM [polycyclic organic matter] emissions of woodstoves.”

The EPA’s mission is to protect human health, and this rule was originally intended to reduce wood smoke pollution to decrease the harmful effects of wood smoke. Unfortunately, we have several reasons to fear that these measures may make things even worse.