Wood Stoves and Air Pollution: What’s the Link?

Wood stoves are a major source of air pollution during cold weather months. The smoke contains pollutants including particulate matter, benzene and formaldehyde that are hazardous to human health. Wood burning also emits more carbon dioxide than coal, oil or gas and is considered the least climate-friendly heating option. The UK, the European Union and US are each taking action to reduce pollution from wood burning stoves and transition to cleaner options.

—

In the US, just under 2% of households nationwide use wood as their primary heating source. However, in some low-income counties such as Arizona’s Apache County, some 60% of households still rely on wood for heating.

Wood stoves are most prevalent in the heavily forested northern regions with Vermont, Wisconsin and Minnesota, the top three states for per capita wood stove emissions.  Northwestern states including Oregon, Idaho and Washington are also in the top 10.

Wood stoves are more common in the UK and European Union, with some 10% of households relying on them. The rate is far higher in Norway, Finland, Switzerland, Poland and other countries with cold winters and abundant woodlands.

Steep increases in energy prices after the start of the Ukraine war in 2022 have led households across Europe to adopt wood as a cost saving measure. Sales of wood burning stoves rose 66% between 2021 and 2023 in the UK and demand for firewood increased 96% between 2022 and 2023 in Germany.

The Carbon Footprint of Wood Stoves

Nearly 50% of timber harvested worldwide is used as fuel and wood burning. The process releases more carbon dioxide, methane, black carbon and nitrous oxide than coal, oil and natural gas do, though emissions are also released when trees are harvested. 

Black carbon contributes to global warming and absorbs solar rays after drifting back to the ground. This can accelerate ice melting and sea level rise in regions such as the Arctic, which is already warming at nearly four times the global average rate.   

Each harvest also represents a missed opportunity for significant carbon sequestration since mature forests have a far greater capacity to absorb carbon dioxide than smaller, immature trees cultivated for harvest within 40 years or less, which never attain full maturity.

Global timber sequestration has declined overall with intensive deforestation. 

Over 10 million hectares of primary forest have been removed primarily for palm oil cultivation in Indonesia and the clearing of one-fifth of the total forest cover in the Amazon has turned the region from the world’s largest carbon sink to a carbon emitter. Emissions from harvesting timber combined with burning results in a net global warming potential that exceeds other fuel sources.

Health Impacts of Wood Smoke

Wood smoke is a significant contributor of the toxic air pollutants particulate matter, benzene, formaldehyde, acrolein and hydrocarbon. Wood burning is the second-largest emitter of wintertime particulate matter (PM2.5), contributing five times more than petroleum refineries, cement manufacturers and pulp and paper plants combined. PM2.5 is the most damaging to human health as it is small enough, at less than 10 micrometers in diameter, to be inhaled and may enter the bloodstream.

Exposure to PM2.5 has been linked with aggravated asthma symptoms, irregular heartbeat, reduced lung function and even premature death in those with existing heart or lung disease. Over 40,000 early deaths per year are attributed to wood burning in Europe and 10,000 annually in the US.

Wood stoves are also a safety risk if not properly used and maintained. Over 14% of house fires in the US are caused by poorly maintained heating equipment and chimneys. Fires resulted in 480 deaths, 1,370 injuries and over US$1 billion in direct property damage between 2016 and 2020, mostly during cold weather months.

Policies and Incentives to Reduce Wood Stove Pollution

The UK, EU and United States have all taken measures to lower the carbon footprint and amount of pollution emitted by wood burning stoves.

Since 2022, all wood stoves sold in the UK and EU must be certified to emit a maximum 375g of PM2.5 for every gigajoule (GJ) of energy produced, while nordic countries have adopted a higher 150g of PM2.5 per GJ standard. This is a significant improvement from older wood stoves that commonly emit over 1,000g of PM2.5 per GJ. 

However, these standards have also drawn criticism as too weak given that other heat sources including oil, gas, electric and heat pumps emit less than 10g of PM2.5 per GJ.

The EU has also taken steps to disincentivize timber harvesting for fuel. In 2022, the European Parliament voted to phase out tax breaks and financial incentives for wood fuel producers. Tiemo Woelken, a German MEP, summarized the case for ending the incentives: “The writing is on the wall: Cutting down forests for energy use is neither sustainable, nor does it help with our energy independence.”

In the US, wood stove emission standards have been set by the Environmental Protection Agency since 1988. The initial standards of 7.5g/hr of PM2.5 (catalytic stove type) and 4.5g/hr of PM2.5(non-catalytic stove type) did not change between 1988 and 2014. In 2020, the EPA completed a major update that strengthened the standard to 2.5 g/hr of PM2.5 for all wood stoves sold in the country. The agency’s estimation suggested that implementing stricter standards could lead to a 70% reduction in stove emissions. This change is projected to yield between $74 and $165 in savings from avoided healthcare expenses and other societal costs for every dollar invested in compliance.

Nonetheless, similar to the European Union, the revised EPA benchmarks and certification procedures have faced scrutiny for their perceived weakness and ineffectiveness. In a damning report released in 2023, the EPA’s Office of Inspector General criticized the wood stove performance standards as “flawed,” highlighted certification processes lacking clarity and affording excessive flexibility, ultimately leading to the certification of wood heaters for sale that emit excessive levels of particulate-matter pollution. 10 states have sued the EPA, urging the agency to address certification issues and further strengthen the emission standards.

The Inflation Reduction Act passed in 2022 by the Biden Administration allocates over $360 billion in funding for clean energy and climate programs. This includes $8.8 million granted to the Northeast States for Coordinated Air Use Management to gather wood stove emissions data that will inform development of a performance ranking for consumers and the next EPA emissions standard for wood stoves.

Government subsidies directly supporting wood stove upgrades have also been implemented. US homeowners can qualify for a tax credit worth 30% of the cost and up to $2,000 per year for upgrading to a new high-efficiency wood burning stove and may also be eligible for an additional $8,000 rebate for reducing household energy use.