19 December 2020

Indoor wood stoves release harmful emissions into our homes, study finds

Log burning stoves are emitting harmful emissions inside the home, according to new research by scientists from the University of Sheffield.

A couple relaxing in front of a indoor woodburner with a dog and glass of red wine
  • University of Sheffield scientists reveal indoor log burners are emitting harmful levels of particulate matter into our homes
  • Particulate matter are tiny solids that float in the air and can cause respiratory illnesses and other health complications
  • Researchers installed air quality sensors into the homes of people with log burners and monitored the levels of harmful particulate matter over a four week period

Log burning stoves are emitting harmful emissions inside the home, according to new research by scientists from the University of Sheffield.

In a study led by Rohit Chakraborty, a Grantham Scholar in the University’s Department of Civil and Structural Engineering, and Dr James Heydon from the University of Nottingham, researchers found that wood stoves certified for indoor use are emitting harmful levels of particulate matter.

Particulate matter are tiny solids that float in the air and have known links to respiratory illnesses[1]. The use of indoor log burners may increase during the Covid-19 pandemic, with people spending more time at home.

Indoor stoves are also popular in the build up to Christmas and over the winter months. However, the study has revealed how they are having a significant impact on air quality inside our homes, which the researchers are keen to stress with vulnerable members of the population, such as children and the elderly, spending more time at home and in one room for extended periods of time.

The researchers installed indoor and outdoor air quality sensors in 20 households with wood/multi-fuel stoves or an open fire, and asked them to record their stove usage over a four week period. The team also asked the participants to record any other emission-producing activities they took part in, such as lighting candles and cooking, which enabled the researchers to distinguish between the emissions produced by their stove and the other activities. In total, the study was based on 260 log burner uses.

Stoves certified by the UK’s DEFRA (Department of Environment, Food, and Rural Affairs) were used by 19 people in the study and one person used an open fire place in accordance with DEFRA regulations - using smokeless coal only. The remaining 19 people used dried seasoned wood.

Results from the study revealed that when the stoves were being used regularly - for approximately four hours - the level of harmful particulate matter pm1 and pm2.5 inside the homes were three times higher than the levels recorded when the stoves were not in use.

The level of harmful matter in the air also peaked for approximately one hour while the stoves were in use. These peak levels occurred when the stove door was opened for refuelling.

The study found that the peak levels of harmful particulate matter in the air were between 250 per cent and 400 per cent higher when participants refuelled their stove more than once during usage compared to one refuel or none at all - meaning some users were experiencing exposure to very high short-term bursts of harmful particulate matter.  

Researchers in the study say these peak levels are also significant because separate, emerging research[2] shows a link between the intensity of particulate matter exposure and respiratory illnesses and other health complications.

The study also found a significant increase in particulate number concentration (PNC) while the stoves were lit, which the researchers say is important because there is uncertainty around the toxicity and size measurement of such particles. There are currently no regulations governing PNCs in the UK.

Currently, the World Health Organisation (WHO) recommends that people are not exposed to more than an average of 25 ug/m3 of the particulate matter pm2.5 over a 24 hour period. The Sheffield research found that people using stoves in the study were exposed to between 27.34 ug/m3 and 195.83 ug/m3 on average over the period in which the stoves were used. The average period of use was four hours, meaning over a short period some people are exposed to very high levels of particulate matter. 

There is no guidance on safe exposure levels to the particulate matter pm1 at the moment.

Rohit Chakraborty, a Grantham Scholar at the University of Sheffield, said: “Our findings are a cause for concern. It is recommended that people living with those particularly susceptible to air pollution, such as children, the elderly or vulnerable, avoid using wood burning stoves.

“If people want to use wood burners we would recommend minimising the time in which the stove is open during lighting or refuelling as that will help in reducing the exposure to the emissions released indoors.

“Over the longer term, we recommend that measures be taken to raise awareness of the risks posed by log burning stoves due to the indoor air pollution they produce. Future research needs to be done on a wider range of stove types and user groups to understand the full extent to which this indoor air pollution is occurring.”

Dr James Heydon, Assistant Professor in Criminology at the University of Nottingham, said: “The study shows that wood burning stoves can expose people to high levels of air pollution while inside their homes. Instead of being seen as a harmless appliance, wood burning stoves should be recognised as having the potential for harm.

“Bursts of particulate matter can enter the home when the stove door is opened, flooding the inside space with air pollution during refuelling. These particles are so small the body struggles to filter them out, making them particularly harmful to children, the elderly and those with respiratory issues.

“Most of our participants were unaware of this as a possibility. More needs to be done to raise awareness of the risks wood burning stoves pose through normal use. People can then make an informed decision on using them.”

Findings from the study suggest that people wishing to continue to use an indoor wood or multi-fuel stove could try to use their stove for shorter periods of time and reduce the number of times they open the stove door while in use to try to reduce the amount of harmful emissions they are exposed to.

Stove manufacturers could look into modifying their designs to limit the level of emissions users are exposed to.

The researchers also acknowledge that the next steps for future research could look at how ventilation affects the level of harmful particulate matter that stove users are exposed to inside their home.

The study, Indoor Air Pollution from Residential Stoves: Examining the Flooding of Particulate Matter into Homes during Real-World Use, is published in the journal Atmosphere from MDPI. To access the paper, visit: https://doi.org/10.3390/atmos11121326

A summary of the research is also available via: https://spark.adobe.com/page/IXMsfspVKUP3e/ 

[1]https://doi.org/10.1016/j.chest.2018.10.042, https://dx.doi.org/10.1016%2Fj.cdtm.2018.04.001, https://doi.org/10.1038/s41598-019-51307-5   


[2] https://doi.org/10.1016/j.atmosenv.2017.04.015https://doi.org/10.1007/s00420-015-1102-6

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