Background
Note: this ruling replaces the version published on 5 November 2025. Following an Independent Review, the assessment has been amended, but the decision remains unchanged.
Summary of Council decision:
Two Issues were investigated, both of which were Upheld.
Ad description
A website for the Stove Industry Association, www.stoveindustryassociation.org, a trade association that represented the UK stove sector, seen on 20 May 2025. The home page included the claim “Choosing a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove”.
A further page, titled “#POSITIVEWOODBURNING CAMPAIGN” stated “There are many sources of air pollution in UK homes including heating, cooking, smoking, scented candles, cleaning & personal care products, and even our pets […] It is important to consider all sources of indoor air pollution in our homes and how they can be reduced […] Used in the correct way, a modern wood burning stove is a very low emission way to heat the main living space in your home”.
Issue
The complainant challenged whether the following claims were misleading and could be substantiated:
1. a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove; and
2. used in the correct way, a modern wood burning stove is a very low emission way to heat the main living space in your home.
Response
1. & 2. Stove Industry Alliance Ltd t/a Stove Industry Association (SIA) explained that they were the UK trade association representing stove appliance manufacturers, suppliers and retailers. The ad was designed to inform the public about the benefits of modern, Ecodesign-compliant stoves when used with appropriately dry or seasoned wood fuel, and other best practice techniques, in contrast to older appliances and open fireplaces. Ecodesign-compliant stoves were those stoves that met the requirements set out in Commission Regulation (EU) 2015/1185 (the Regulation). Under that legislation, the only emissions from stoves that were regulated were particulate matter (PM), carbon monoxide, nitrogen oxides, and organic gaseous compounds (OGCs). They explained that under UK law, a stove must achieve a minimum efficiency of not less than 65%, and an open fire must achieve not less than 30%. Since emissions levels were limited, efficiency and emissions were directly correlated – the more efficiently wood fuel was burned, the fewer unburned particulates and gases were emitted for every unit of heat delivered. That meant a modern stove was more efficient and less polluting than an open fire.
SIA highlighted that both claims under investigation had been qualified with the phrases “can significantly” and “used in the correct way”, to ensure they were not interpreted as absolute claims. They highlighted that non-government organisation (NGO) and consumer advice in the sector framed “emissions” as referring specifically to visible smoke and PM – and the claim “lower emissions” was intended to refer to those emissions. They explained that to avoid over-generalisation across every pollutant type, they had intended the “very low emission” claim as relating to PM emissions when stoves were Ecodesign-compliant, correctly operated, and fuelled with 10–20% moisture wood. They used the term “dry wood” in the ad to refer to wood with a moisture content of between 12% and 20% and said it would be understood by consumers as being synonymous with the term “seasoned wood”. They said the average moisture content of wood sold by their members was between 9% and 12%.
SIA said modern stoves were low emitting when compared to open fireplaces or older solid fuel local space heaters – the latter was a heater that heated the space in which it was installed only. A few open fireplaces would produce a lot more emissions and lower useful heat output than a greater number of modern stoves, so the absolute emissions for both technologies may look similar when assessing data on overall emissions from both heating sources, but the effective outcomes were very different. For example, the UK National Atmospheric Emissions Inventory (NAEI) – which estimated aggregate national annual pollutant emissions from 1970 to the most current publication year for the majority of pollutants – appeared to show that emissions of certain pollutants were higher in Ecodesign stoves burning dry wood than the other heat sources cited in the ad. That comparison was based on aggregate emissions by emission source and did not indicate that an individual Ecodesign stove would emit more of those pollutants than an individual older stove or open fire. The SIA explained that while the aggregate emissions of some toxins were higher in modern stoves than open fireplaces, the overall PM and smoke emissions profile had substantially improved over time. They said the Informative Inventory Report that accompanied the NAEI data stated there had been a reduction in PM2.5 emissions from small combustion in recent years. In their view, the more appropriate method of comparison was per-unit laboratory testing.
In support of the claim “a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove” they provided a letter dated 2 April 2025 sent to them by the Ministry of Housing Communities and Local Government, the above-referenced report from the NAEI with accompanying data set – published in 2024, guidance documents on wood burning from the London Assembly and the Department for Environment, Food & Rural Affairs (Defra), Commission Regulation (EU) 2015/1185, a report they had commissioned titled ‘Comparative Smoke Emission Tests’, and a blogpost authored by Stiftelsen for industriell og teknisk forskning (SINTEF) and published on 8 February 2024.
In support of the claim “Used in the correct way, a modern wood burning stove is a very low emission way to heat the main living space in your home” they provided a literature review they had commissioned – completed in April 2022, a project report from Imperial College London published in September 2023, a report from the European Committee of Manufacturers of Domestic Heating and Cooking Appliances published in June 2025, information related to Standard Assessment Procedure 10 (SAP 10), a factsheet from wood fuel industry body Woodsure published on 21 January 2025, and an article from a national newspaper published on 2 May 2025.
Assessment
The CAP Code stated that the basis of environmental claims must be clear. Unqualified claims could mislead if they omit material information. Comparative environmental claims such as “greener” or “friendlier” could be justified if the advertised product provided a total environmental benefit over that of competitor products and the basis of the comparison was clear.
1. Upheld
The ASA understood that the SIA had used the term “modern stove” to refer to stoves that complied with the provisions of Commission Regulation (EU) 2015/1185 (the Regulation), part of assimilated EU law, which set out “ecodesign requirements” for solid fuel local space heaters, aimed at reducing their environmental impact.
The ad stated “a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove”. We considered consumers were likely to understand “emissions”, which in the context of the ad had been used in a general, and non-specific manner, as referring to polluting greenhouse gas (GHG) emissions, and other air pollutants such as particulate matter (PM). It was not clear from the ad that the claim was intended to be limited to emissions linked to the Regulation.
The NAEI data showed aggregate national emissions by source category and fuel type. While the data appeared to show higher aggregate emissions for some pollutants from modern stoves than from open fireplaces or older stove types, those figures were influenced by the number of appliances in each category. It therefore did not provide a direct per-appliance comparison between modern stoves, open fires and older stoves, or indicate the emissions performance of an individual stove type in any category.
We assessed the further evidence provided by the SIA. The letter from the Ministry of Housing Communities and Local Government stated its understanding that it was possible to significantly reduce the amount of smoke emitted through domestic burning when the correct fuels, appliances and practices were used. The London Assembly guidance for wood burning in London stated that open fireplaces were the most polluting way to burn solid fuels, and that wood with a lower moisture content was preferable as a source of fuel to fresh logs. Defra guidance on reducing the negative environmental impact of stoves and open fireplaces suggested the use of an Ecodesign stove as an alternative to an open fireplace or older stove. The guidance also stated that both open fireplaces and wood burning stoves were major contributors to PM2.5 pollution.
We next reviewed the report commissioned by SIA, entitled ‘Comparative Smoke Emission Tests’, and the report commissioned by Defra related to emissions factors for domestic solid fuels. The SIA report compared smoke, general PM, methane, and carbon dioxide emissions for modern stoves with those from open fireplaces and older stove types. The study was done under laboratory conditions using 2.5 kg of wood with a moisture content of between 12.4% and 12.8%, and showed the modern stove emitted lower per-appliance levels of each pollutant than open fireplaces and older stoves. The Defra-commissioned report stated that, for the Ecodesign-compliant stove tested, “seasoned wood” with a moisture content of 15% produced lower emissions than very dry wood (with a moisture content of 10% and under) or wet wood (with a moisture content of 21% and over). The blogpost, from Stiftelsen for industriell og teknisk forskning, a Norwegian research organisation, set out their case for updating the Norwegian national emission inventory relating to wood burning stoves. It showed a reduction in PM2.5, carbon monoxide and methane emissions between modern and older stoves, but did not include open fireplaces, nor the conditions under which the testing was conducted.
Some of the evidence provided showed modern stoves could produce less PM2.5 than older stoves when burning wood of a specific moisture content, and we acknowledged SIA’s comments that they had intended the claim to relate to the findings in relation to PM 2.5 and black smoke. However, the relevant emission types had not been included in the ad, which also referred only to “dry wood” without qualification. In addition, the claim relayed general information to stove owners and consumers interested in buying a new stove, who, given the lack of clarification about the context of the claim or the circumstances in which it applied, were likely to have an expectation that the claimed effects would apply to them. In addition, we had not seen evidence that the results achieved under laboratory conditions would be replicable in the real-world use of modern stoves, or were representative of how consumers used the stove type. The evidence therefore did not substantiate the claim as it appeared in the ad, nor the claim that SIA said they had intended to make (i.e. to refer to PM 2.5 and black smoke only).
We concluded the claim “a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove” had not been adequately qualified or substantiated.
On that point, the ad breached CAP Code (Edition 12) rules 3.1, 3.3 (Misleading advertising), 3.7 (Substantiation), and 11.1 and 11.3 (Environmental claims).
2. Upheld
We considered consumers would understand the claim, in the context of the ad, as meaning that when used in line with good practice as a means of heating an area such as a living space, a modern stove would produce a very low level of indoor emissions compared to other methods of heating that same space. They would understand “emissions”, which in the context of the ad had been used in a general, and non-specific manner, as referring to polluting GHG emissions, and other pollutants such as PM. They would likely understand “very low emissions” to mean emissions were minimal. We expected to see evidence to demonstrate that modern stoves were a “very low” emissions emitting source of home heating.
We assessed the evidence provided by the SIA. The Woodsure fact sheet set out questions and answers about wood burning using modern stoves, including about air pollution from burning solid fuel, national PM2.5 emissions from wood burning and government action to reduce emissions from the practice. The newspaper article stated that there had been an increase in the number of homes with stoves since 2022, and that increase had led to “air pollution hotspots” in urban areas outside major cities. The Standard Assessment Procedure 10 (SAP 10) was a methodology for assessing energy performance in domestic dwellings. That evidence did not show that modern stoves, when used correctly, would produce “very low” levels of indoor air polluting emissions compared to other methods of heating a living space.
The report from the European Committee of Manufacturers of Domestic Heating and Cooking Appliances, a trade body representing European domestic heating appliance manufacturers, set out the future role of wood burning as a source of heating in the EU. The report made no finding on indoor air pollution from modern wood burning stoves.
The literature review commissioned by SIA surveyed studies on the contribution of different types of wood burning stoves to indoor PM emissions. The review ostensibly found PM concentrations in houses using wood burning stoves was below the World Health Organisation (WHO) recommended 24-hour exposure value. However, the review also stated that according to the WHO there was no safe level of PM exposure. It further stated that factors such as stove quality, wood quality, and location factors as well as user behaviour could impact indoor air quality, but that information was rarely included in the reports reviewed. The literature was unpublished and had not been peer-reviewed.
The project report from Imperial College London related to PM emissions from domestic wood burning. Among other things, it compared PM2.5 emissions between open fireplaces, Defra exempt stoves (stoves that could be used in smoke-controlled areas) and non-exempt stoves, and a clearSkies Level 5 certified stove (Ecodesign-compliant). It found that indoor PM2.5 levels typically increased during lighting and refuelling, but that increases in indoor PM2.5 concentrations may be more affected by how the appliances were used and the airflow characteristics of the appliance, rather than the type of appliance or fuel used. The report made no findings on other emissions types, and we had not seen evidence to demonstrate that the findings in relation to the clearSkies Level 5 certified stove would be applicable across all modern stove types.
We concluded the basis of the comparison “a very low emission way to heat the main living space in your home” had not been made clear, and also had not been adequately substantiated as consumers were likely to understand it.
On that point, the ad breached CAP Code (Edition 12) rules 3.1 (Misleading advertising), 3.7 (Substantiation), 11.1 and 11.3 (Environmental claims).
Action
The ad must not appear again in the form complained of. We told Stove Industry Alliance Ltd t/a Stove Industry Association to ensure that all objective claims were adequately substantiated in future ads and that appropriate qualification was used to explain the limitations of claims where relevant. We reminded them that the basis of comparative environmental claims must be made clear.
