Indoor pollution from wood burning doesn’t get as much attention as outdoor emissions, but it can be quite significant.
Earlier this year, Green Global Future in Denmark measured the indoor particle and black carbon emissions (PDF) from a wood stove burning dry wood in a typical living room.
Green Global Future noted that indoor pollution from wood stoves can spread throughout the entire house, including into children’s bedrooms, and do so during times of year when ventilation is limited and people are spending more time inside.
Emissions measurements have been carried out previously by the Danish Building Research Institute in 2012, Green Transition Denmark in 2017–18, and by students at the Technical University of Denmark in 2021, who all found that new eco-labeled wood stoves can cause high indoor air pollution levels.
Notably, it has been found (PDF) that new eco-labeled wood stoves do not pollute the indoor environment less than old wood stoves.
Despite this, Green Global Future notes, there are no indoor emissions requirements for new eco-certified wood stoves.
The owner of the house—“a typical residential home in Gentofte close to Copenhagen”—was instructed to use the wood stove the way he normally would. Dry beech firewood was burned.
During the measurements, however, the house was vented several times—something the homeowner typically doesn’t do when burning wood. This “significantly” lowered the recorded pollution levels.
The measuring devices were placed in the living room, at the usual distance from the wood stove where the residents would normally sit.
Measurements were started 20 minutes before kindling and stopped around 4 hours later.
Other sources of pollution were avoided during that timeframe so the measurements would only reflect what was being emitted by the wood stove.
The results?
“Very high levels” of ultrafine particles, fine particles, and black carbon were measured. Ultrafine particle levels in the living room were found to be 10–15 times higher than what would typically be found during rush hour on “the most polluted streets in Copenhagen”; fine particle levels were around 100 times higher.
Peaks in pollution levels occurred even when wood was not being added, suggesting that pollutants leak from the stove even when the door isn’t open. “The same observation was seen for many stoves in previous studies.”
According to Green Global Future, these measurements confirm that a wood stove can pollute the air inside homes “to extremely high levels with hazardous ultrafine particles, fine particles and black carbon (soot).”
It was pointed out that during a previous investigation in 2023 by Denmark’s Healthy Indoor Environment, it was found that wood stove users couldn’t smell the wood smoke emissions inside their homes. Therefore, smell is not an effective indicator to warn when pollution levels are high.
Green Global Future offered a concluding recommendation, among several others, that new wood stoves be sold with warning labels: Use of this stove can cause high levels of toxic pollution in your home.
A brief with further information is available on Green Global Future’s website (PDF).
Green Global Future has joined our coalition, and is now a member organization of DSAWSP.
