Woodburners – the real facts: the Impact of wood burning stoves on indoor air quality

You may well have seen over the 2020 Christmas period a number of newspaper articles about wood burning stoves.

One article was based on a report published by ‘Atmosphere’ on 7th December by Sheffield and Nottingham universities entitled ‘Indoor air pollution from residential stoves’ and most recently an article in most of the major nationals in which the British Lung Foundation and Asthma UK (now a combined organisation) added their voice to the mix. Dr. Nick Hopkinson, medical director of Asthma UK was quoted in the articles as saying “To protect yourself and others …, avoid buying a wood burning stove or using an open fire if you have another source of fuel to cook and heat your home with”

Misconception: Wood burners cause around 40% of outdoor particular matter

The latter articles quotes: “We know that burning wood and coal releases fine particulate matter (PM2.5) – the most worrying form of air pollution for human health” and that around 40% of outdoor particulate matter is caused by woodburners, coal fires and open fires.

This fact is completely wrong. A more accurate percentage is less than 10%. Have a quick watch of this video to clearly understand the misconceptions that are still flying around the media despite Defra agreeing that the figure is incorrect! – https://youtu.be/9VQnSgquvp0

Also, important to note on this point is that at present more than 50% of wood is still burnt on a 10-year old stove or open fire. If these appliances were converted to a modern clearSkies approved appliance, the emissions would be reduced by at least 45% to a level less than 5% of overall emissions.


Questionable data accuracy

The articles from Sheffield and Nottingham Universities reported in the ‘Atmosphere’ publication appear to have some fundamental problems in respect of lacking a basic understanding of the operation of a wood burning stove. There are also other factors that will influence indoor air quality within the house and their comparative scale of creating particulate matter, and they draw emotively worded conclusions that are not supported by the evidence provided.

Furthermore, the air quality monitors used in the research were “low-cost” and their accuracy is highly debatable.  The report itself identifies the accuracy of the equipment used and the fact they weren’t calibrated at all during the collection of the data as a potential limitation of the research.  Given this fundamental point, it is hard to understand how the research reaches such firm conclusions, when the data accuracy is questionable.

Throughout the report the phrase “flooding” of particulate matter is an emotive one and not one based on scientific fact.  It clearly suggests a predetermined outcome being justified, given the facts presented do not support the conclusion.

The research does not address the building regulations requirements for a specified number of air changes per hour in habitable rooms and does not measure whether appropriate ventilation was in place.


Influence of other factors on indoor air pollution

The research doesn’t seek to explain how other factors influencing indoor air pollution have been excluded to sufficiently separate out the impact of a wood burning stove.  For example, the fact the indoor air pollution arises between 6pm and 10pm is taken as clear evidence that this pollution comes from the stove.  However, this is also typically the time of maximum human activity and movement in a home which will contribute to indoor air pollution, and activities such as cooking, using the toaster, burning candles etc.

There is also no comparative data presented in the research for other causes of indoor air pollution such as:

  • Cooking, particularly roasting or frying
  • Using a toaster
  • Cleaning – particularly dusting or hoovering
  • Use of indoor candles
  • Use of aerosols

Previous research has indicated these create far higher peak levels of indoor air pollution than a modern Ecodesign compliant stove.

Interestingly in February 2016 and again in Oct 2018, Harry Wallop wrote articles in the Telegraph and Times where he borrowed instruments to measure the PM2.5 particles during his everyday activities. Government guidelines suggest that a reading below 35ug/m3 is ‘low’; by contrast, ‘very high’ is above 72ug/m3.

His home had a steady reading of between 18ug/m3 and 22ug/m3 – well within the limits but proof that a normal person’s home is full of far more dust, soot and rubbish than one thinks.

On the tube trip to work, levels did not fall below 125ug/m3 and when the doors opened at Kings Cross, it peaked at 309ug/m3!

His wood burning stove, albeit not the latest Ecodesign compliant stove was reading a steady 42ug/m3 but as he only used it at weekends he had little concern. However, when he burnt the toast, the reading spiked at 10,000ug/m3 and even an hour later it was still above 300ug/m3.

In his later article it was the cooking of the bacon that really raised the reading and way higher than his wood burner.


“We must look at the bigger picture.”


It was also heartening to read a more positive article in the Telegraph on 28th December in which Jessica Salter wrote an article entitled ‘Sales of log burners are booming – and they can still be eco-friendly’. In addition the Guardian recently printed a readers letter in which a Mr Peter Perry from Cornwall makes a very valid point that we must look at the bigger picture. He wrote “undoubtedly if we look closely enough, there are negatives in using wood burning stoves for domestic heating, but there are also many positives, and we need to hear the whole story. So, I’m hoping that, in due course a second study will carefully assess and quantify the benefits, both physical and emotional, and that these will be duly reported by the Guardian”.

Here’s the best practice advice to follow to minimise any indoor air pollution from a wood-burning stove:

  • If possible, install an Ecodesign compliant stove or even better one with a certified clearSkies label as explained above
  • Ensure you burn only dry wood, such as “Ready to Burn” certified kiln dried wood
  • Only refuel your stove when the logs have been fully burnt and the fire-bed is down to embers
  • Fully open all air controls on the stove; wait for 30 seconds then carefully open the stove door by a small amount and pause briefly before slowly opening the door to allow refueling. These steps allow the air pressure in the stove to equalise with the room pressure, much reducing the chance of any smoke spillage into the room
  • Do not overload the stove and follow the manufacturer’s instructions
  • Ensure your room is properly ventilated in accordance with the stove manufacturer’s instructions and Building Regulations

 Are woodburning stoves really a major cause of air pollution?

The Stove Industry Alliance (SIA) has a great video to help consumers understand the facts about woodburning stoves.

Modern woodburning stoves and fireplaces ensure low emission and low carbon heating for our homes using truly sustainable and renewable fuel. However, over the last two years, through a number of media reported misconceptions and a lack of awareness, these appliances have often been portrayed as negative and responsible for contributing far more particulate emissions than they actually do.

This new SIA video has been produced to dispel these reported myths around woodburning stoves by addressing three of the major misconceptions that have so often been mis-quoted by the media.

The first misconception is the idea that woodburning stoves are the biggest contributor in the UK of small particulate matter. At the root of this myth is a statement from Defra’s Clean Air Strategy claiming that domestic combustion accounts for 38% of fine particulate matter. This number was based on a survey carried out by the government in 2015 (1) which wrongly over-estimated the amount of wood being burnt in the UK on stoves and fireplaces.

A much bigger survey carried out in 2019 by the SIA (2) showed the actual figure was less than a third of what the government quoted, making the percentage of PM.2.5 that could be attributed to domestic combustion closer to 13% and NOT 38%.

Also, the 38% figure stated by Defra is based on emissions from older stoves and open fires and it is known that modern Ecodesign compliant woodburning stoves produce 66% less emissions than these outdated appliances. Defra also includes other sources of PM2.5 in its overall estimation, including wildfires, bonfires, and incinerators which are not insignificant and certainly unregulated sources of particulate matter.

One of the most striking myths claimed about woodburning stoves is that they “create the same emissions as 18 diesel cars”. This comes from test results interpreted by the Air Quality Expert Group (AQEG) but their comparison is extremely misleading and, as the video points out, is like comparing apples with oranges.

Firstly the comparison is between the appliances running at significantly different efficiency levels, by measuring a car exhaust emissions at an efficient run rate of 21mph and comparing them to all of the emissions at a full run rate for a stove. This completely ignores all the small particle emissions from the car’s brakes and tyres, when frequently the emissions from a car’s brakes and tyres are actually greater than the emissions from the exhaust pipe! Finally the difference in the dispersal point of particulate matter from woodburning stoves to cars is ignored completely. A car outputs its emissions at face level for a child and therefore there is very little dispersal before it is breathed in, whereas a woodburning stove sends its emissions out of the top of the chimney and there is considerable dispersal of emissions before they even reach human height.

The last myth shown by the SIA’s video is the concept that all woodburning stoves and fireplaces are harmful. Chair of the Stove Industry Alliance, Morley Sage, explains why this is one of the more concerning misconceptions: “This view fails to take into account the huge advances that have been made by the woodburning stove industry in recent years. Many critics of woodburning stoves base their assumptions on data linked to open fires, older stoves and poor-quality wood fuel. The SIA would be one of the first organisations to point out that burning wet wood on an open fire, a practice that is still very common today, is one of the least efficient and most highly polluting ways to heat your home. By stark contrast, a modern woodburning stoves emits up to 90% less emissions than an open fire and up to 80% less than a stove that is 10 or more years old.”

Members of the SIA were among the first manufacturers to develop the technology within their appliances to achieve the forthcoming Ecodesign Regulations (SIA Ecodesign Ready), and more recently the SIA has supported and initiated the launch of clearSkies, an independent emissions and energy performance certification scheme for solid fuel stoves and fireplaces. Appliances that are certified under clearSkies will not only meet the performance levels set out under Ecodesign, but also many go a significant way beyond. We would therefore encourage you to look for the clearSkies certification mark when looking to buy a new stove or indeed move from an open fire to a modern stove.

The true facts about modern woodburning stoves are they are a highly efficient, future proof, and very low carbon and sustainable way of heating your home and keeping our families warm, and that is something to be proud of.

For further information on owning, using and maintaining a wood burning stove visit www.stoveindustryalliance.com

1) The BEIS Domestic Wood Survey https://www.gov.uk/government/publications/summary-results-of-the-domestic-wood-use-survey using a sample size of 1,206

2) SIA independently verified research carried out in 2019 using sample size of 10,620 using same questions as BEIS survey

 Fire cement – its uses and limitations

Fire Cement is a ready-to-use putty which is heat resistant up to 1250oc. There are a number of manufacturers and brands and it’s available in different sizes in both black and cream. The cement can be used to seal joints in wood stoves, especially around the area where the flue rises out of the top of the stove. It can also be used to repair firebricks. Fire cement when dry is a non-flexible solid sealant (unfortunately “high temperature” flexible silicone sealants degrade above 300 degree Centigrade which is above the normal operating temperature of your stove). The expansion and contraction of your metal stove as it heats up and cools down will inevitably crack any fire cement around joints on the flue and stove pipe.

Cracks in fire cement, or even where it has fallen out, are only a critical issue if smoke is coming through. Assuming your flue and stove are correctly installed and properly maintained, the negative pressure within the flue will draw smoke and fumes up your chimney, preventing any problems and any smoke coming out. But do remember to have your Carbon Monoxide alarm properly located and test it regularly; it provides an immediate warning of any problems.

It’s a routine and simple job to redo the joints with inexpensive fire cement (typically £2.50 for a small tub). First ensure the area is clean, free from dust and rust. To use, wear a latex glove and apply a liberal amount of cement on one finger. Then work the cement well into the cracked or damaged area. As soon as possible, gently heat dry the repaired surfaces, gradually raising the heat to full operating temperature over 3-4 hours. Apply further cement to any fire cracks that may appear.

Use straight from the tub! We always have stock of fire cement in our showroom.


Fire Cement



 Lime mortar and plaster for fireplaces

As part of our stove installation service and where we are “knocking out”, enlarging or building a fireplace, we can offer the option of having the fire opening rendered in Lime (to be precise that’s a base coat of a lime and hemp mix with a lime plaster finish coat).

Lime is a traditional building material with a number of advantages over modern materials:

– it breathes and lets moisture out so is particularly suitable for Victorian brick buildings and older Cotswold stone buildings which don’t have cavity walls or damp courses.
– any small cracks that appear as a building settles, typically get sealed up naturally as the lime mortar/plaster re-carbonates (Lime does not “dry out” in the way we’re used to with modern materials. It sets through a process of carbonisation as it is exposed to Carbon Dioxide CO2 in the air)
– lime is a softer material than modern cement and plaster which means it will give rather than cracking Cotswold stone
– it is a traditional material free of any chemicals, particularly suitable for older buildings and new environmentally friendly buildings. It is usually required for any Listed building.
– using Lime to render a fireplace takes no longer than using sand and cement


There’s one thing to watch out for when choosing to have a fireplace rendered in Lime. Lime takes longer to set through the process of carbonisation than the time sand and cement takes to dry out. So, to minimise the risk of plaster cracking, instead of recommending the stove in a newly rendered fireplace isn’t used for 1 week, we recommend the stove isn’t used for 4 weeks.

 Is the Government going to ban woodburning stoves?

Err, no. Not at all.

We really shouldn’t be surprised anymore at how news headlines often distort facts, but the negative publicity about the really positive things included in the Government’s consultation paper published in May 2018 on its 2018 Clean Air Strategy has certainly been puzzling!!

The full story is here: https://consult.defra.gov.uk/environmental-quality/clean-air-strategy-consultation/ and Chapter 6 is the interesting section on “Domestic burning”

Here’s our summary of the key points:

1. Good news – from 2022 only new efficient, high-performance woodburners can be sold. But there’s no suggestion that existing woodburners installed before 2022 cannot continue to be used. Many of these “Ecodesign 2022” stoves are already available; the difference in performance between an Ecodesign stove and a standard woodburning stove is staggering (need convincing? Come and see one in action at our showroom in Stroud).
2. Good news – suppliers will be stopped from mis-selling firewood that they claim is dry or seasoned when they can’t demonstrate it’s actually ready to burn with a moisture content of 20% or less (the plan is that this won’t apply to “bulk” deliveries of firewood for people to dry/season themselves; it’s mainly targeted at garage forecourts etc selling nets of unseasoned logs. Sound familiar?)
3. Good news – local authorities will get new powers to clamp down on illegal domestic burning eg open fires burning wood in urban areas. Open fires and bonfires are absolutely the biggest source of pollution from wood smoke, not properly used woodburning stoves. Local authorities already have some powers to do this but enforcement is difficult and smoke control zones are out of date as towns/cities have developed
4. Good news – certain types of coal with high levels of sulphur emissions when burnt will be banned
5. Good news – people with woodburning stoves are encouraged to get them serviced and swept regularly

What’s not to like?

The government is inviting anyone who’s interested to comment on their proposals before 14/8/18 (just follow the link above to the consultation document).


 I’m not sure how much firewood I need to order to last me over the winter?

We have a rule of thumb which may be helpful. Many of our customers who use their woodburner a few evenings a week over the winter, order 2 cubic metres for the winter. If you use your woodburner most evenings, you’ll probably need 3-4 cubic metres. If you use your woodburner all of the time, day and evening, then maybe 6 cubic metres or more.

Please remember this does of course depend on the output and efficiency of your woodburner, as well as the type of firewood you’re ordering (for example a cubic metre of kiln-dried hardwood provides more heat than a cubic metre of seasoned softwood).

If you have an open fire, because they are so inefficient, you’ll need at least 3 times the amount of firewood you’ll use in a woodburner to get the same amount of heat.


 Delivering to us is not straightforward, how do I arrange this with you?

As part of the checkout process, there’s a section where we ask you to tell us about any special arrangements we need to make for your delivery.

 What’s your lead times for delivery?

We can usually deliver within a couple of days but this does of course depend on how busy we are. Sometimes we can add orders onto delivery runs we already have planned and get to you the next day (or even the same day!).

 When ordering online, how do I know when delivery will be?

As part of the checkout process, there’s a section where we ask you to tell us your preferred delivery date(s). We’ll contact you to confirm the delivery day and approximate time and will do our best to get to you when you prefer.

 Do I need to be there when you deliver?

Not if you can give us some specific instructions on where you’d like us to leave your firewood. If you’re not going to be at home, please let us know so we won’t try contacting you on the day of delivery to let you know we’re on our way.

 How many nets of logs in a cubic metre?

We pack one cubic metre of logs into 20 good size nets (net size is 450mm x 700mm).

 What does the moisture content mean?

Moisture content is an effective measure of how well the wood will burn. Soggy, unseasoned wood will smoke and cause your flu to become lined with tar and soot, reducing its effectiveness and also making it a very real chimney fire risk. Here at Elcombe Fire & Wood we guarantee that all our seasoned wood has a moisture content of less than 25%, so you can be assured of a hearty, roaring fire.