Joint press release by the German Environment Agency and the State Agency for Nature Conservation, Environment and Geology for the State of Hesse

Blue Angel for wood-burning stoves: Dust precipitators can reduce ultrafine particles by 97 percent

HLNUG investigates the emission of dust and ultrafine particles

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Fine dust particles from wood burning has dire consequences for human health
Source: focus finder /

Wood-burning stoves have been experiencing a renaissance for some time now. There are more than eleven million “single-room combustion systems” in Germany. In fact, around 200,000 new stoves are sold every year, most of which are purchased to replace old appliances. While some buyers aim to avoid the high energy prices, others appreciate the wood fire as a cozy source of warmth. However, stove exhaust gases have a negative impact on air quality and human health. Burning wood produces harmful pollutants such as fine dust, soot, PAHs (polycyclic aromatic hydrocarbons) and nitrogen oxides.

As part of a research project funded by the German Environment Agency (UBA⁠), the Hesse State Agency for Nature Conservation, Environment and Geology (HLNUG) investigated the emission ⁠of ultrafine particles (UFP) and the effectiveness of electrostatic precipitators to reduce fine dust emissions from a wood-burning stove. Findings: Dust and UFP emissions can be significantly reduced with the help of an integrated precipitator. The model tested achieved a 97 percent reduction in the number of ultrafine particles.

The research project aimed to validate a new measurement technique designed to quantify fine dust particle levels. This method was developed specifically for the Blue Angel eco-label for wood-burning stoves (DE-UZ 212) and for retrofit dust precipitators (DE-UZ 222). To this end, the measuring method for determining the number concentration of ultrafine particles in stove exhaust gas was tested at the HLNUG stove test bench in Kassel in collaboration with seven other laboratories from Germany, Denmark and Switzerland. The measured values from the various test laboratories showed that the measurement method was able to reliably assess the number of particles. There are now no obstacles to implementing the measurement method for determining particle number concentration as a compulsory aspect of the Blue Angel eco-label  wood-burning stoves and dust precipitators.

In the course of validating the measuring method, the potential of an electrostatic precipitator to reduce ultrafine particles and fine dust was also investigated. For the commercially available stove used, an average emission reduction of 97 percent was achieved for the particle number concentration (UFP) and 84 percent for the particle mass concentration.

UFP, or ultrafine particles, refers to dust particles, which are smaller than 100 nanometers. For comparison, it would take more than 10,000 ultrafine particles to cover a distance of one millimetre. UFPs are the smallest solid and liquid particles in our air. Such ultrafine particles are produced during combustion processes, such as in a wood-burning stove, for example. These particularly small fine dust particles pose a potential health risk. Unlike larger fine dust particles, their small size allows them to penetrate very deeply into the lungs and enter the bloodstream. UFPs are suspected of causing a wide range of illnesses such as bronchitis, asthma and cardiovascular diseases.

Replacing old wood-burning stoves with new ones bearing the Blue Angel ecolabel leads to a decrease in fine dust emissions and thus to a reduction in the environmental and health impact of these stoves.

In addition to the legal requirements regarding the type test for wood-burning stoves, the Blue Angel eco label further requires that stoves have significantly lower dust, carbon monoxide and volatile hydrocarbon emissions and that this must also be true for the high-emission ignition phase.

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