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.
I see the SIA reviewed some studies on the apparent relaxation & health benefits of wood stoves. But, surely, some of that could just be about feeling sleepy at the end of a busy day, in a warm safe environment, with one’s feet up and a soothing background noise blocking out anything else such as passing traffic or voices from somewhere? You could get just the same effect from immersing yourself in watching a calming nature video? I looked up studies of the kind the SIA focused on. I found they were either retrospective questionnaires or lab tests that didn’t involve anyone sitting in front of real wood burning at all. The participants just watched a film of gentle flames with sound effects, or saw a gas fire through a screen. They were not exposed to air pollution from a stove at the time. Furthermore, as far as I know, real combustion requires a steady supply of oxygen. That means a real wood stove can begin to deplete the oxygen levels in a small or poorly ventilated room. I think that could very well give rise to a buildup of harmful particles and gases in the room, including carbon monoxide, which could be dangerous. Also, I’ve just read on the internet that “fireplaces can make you sleepy by generating warmth that relaxes your muscles and from the “white noise” generated by the burning firewood”. Fires are also usually lit at nighttime, after the last meal of the day and when it has become dark, both of which trigger your body to go to sleep. So, i a stove or fireplace makes you sleepy and relaxed feeling, perhaps it is simply because they make you warm and reduce the oxygen around you? I know too that warmth is used to treat sore muscles after workouts – and that can dilate your blood vessels. The warmth then makes your muscle fibres more elastic, and might help your nerve endings to block any aches and pains from the day. But it doesn’t have to be a wood stove to do this, that’s the point.
Am I right that ultrafine particulates are not measured at the factories that make these new ecostoves? Or maybe the levels are not reported? The no wonder that the stove companies and the SIA hardly ever mention them? Is there a safe level for UFPs? We only hear about PM2.5/10. Presumably, unlike “normal” wood smoke, UFP emissions are not even visible? Good article, thank you. I’d like to pin this up at my GP surgery but I bet I won’t be allowed to.