A new study by the University of Surrey’s Global Centre for Clean Air Research (GCARE) has challenged the assumption that manufactured fuels are the cleanest choice for use in domestic stoves.
The GCARE study looked at indoor air quality in homes using open fireplaces and improved wood-burning stoves, burning a variety of fuel types.
This study assessed how different wood stoves and solid fuels affect indoor air quality in five homes in Guildford during winter. It focused on emissions of ultrafine particles (UFPs), PM2.5, PM10, black carbon (BC), and carbon monoxide (CO).
It was seen that during wood-burning periods, PM10 levels rose by 12 times in homes with open fireplaces and three times with improved stoves, compared to non-burning periods. Pollutant spikes were most severe during fire lighting, refuelling, and ash cleaning.
Ultrafine particle (UFP) exposure was highest in open fireplace homes, especially those with smaller rooms and long burn durations. Even modern eco-design stoves showed high UFP levels when used as the main heat source in smaller living spaces.
The study also found that manufactured fuels like wood briquettes and smokeless coal emitted more pollution than seasoned or kiln-dried wood, despite being marketed as cleaner alternatives.
PM2.5 levels were up to 4.1 times higher with wood briquettes, due in part to the ignition process that requires multiple firelighters – another source of emissions.
Improved stoves provided better thermal comfort (average 21.3°C) than open fireplaces (17.7°C) and lower humidity levels. However, in winter, limited ventilation due to closed doors and windows contributed to pollutant buildup, as all homes recorded low air change rates.
The study concludes that longer burn times and smaller room volumes significantly increase exposure risks, even with modern stoves and cleaner fuels. It recommends short-term stove use, good ventilation, and possibly air purifiers as practical interventions. Importantly, the findings challenge the assumption that manufactured fuels are cleaner and suggest kiln-dried wood as the least harmful option tested.
Professor Prashant Kumar, Founding Director of GCARE and corresponding author of the study, said: ‘With rising energy prices, many households will be turning to solid fuel heating when the colder months hit, often assuming that modern stoves offer a cleaner, safer alternative. However, our findings show that this shift comes at the cost of indoor air quality, with potentially serious health implications considering people spend up to 90% of their time indoors. Public health advice, ventilation guidance, and building design standards must adapt to keep pace with these changing heating habits.’
Abidemi Kuye, PhD researcher at the GCARE, said: ‘Even in homes using ‘cleaner’ stoves and fuels, we saw pollutant levels rise well beyond safe limits – especially when ventilation was poor or stoves were used for long periods. Many people simply don’t realise how much indoor air quality can deteriorate during routine stove use. This research shows the need for greater awareness and simple behavioural changes that can reduce exposure.’
The full research can be read here.
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