Background
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:
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a modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove; and
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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. 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%.
SIA said modern stoves were low emissions when compared to open fireplaces or older solid fuel local space heaters. 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 but the effective outcomes were very different. Comparing like-for-like usage data from the UK National Atmospheric Emissions Inventory (NAEI), which estimated annual pollutant emissions from 1970 to the most current publication year for the majority of pollutants, showed that while aggregate emissions of some toxins were higher in modern stoves than open fireplaces, the overall particulate matter (PM) and smoke emissions profile was substantially improved. They said the Informative Inventory Report that accompanied the data stated there had been a reduction in PM2.5 emissions from small combustion in recent years. Although, in their view, the correct method of comparison was ultimately 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 sent to them by the Ministry of Housing Communities and Local Government, the above data set and report from the NAEI, guidance documents on woodburning from the London Assembly and the Department for Environment, Food & Rural affairs (Defra), a piece of EU legislation, an independent report they had commissioned, and a blogpost.
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, a project report from Imperial College London, a report from the European Committee of Manufacturers of Domestic Heating and Cooking Appliances, information related to Standard Assessment Procedure 10 (SAP 10), a factsheet from wood fuel industry body Woodsure, and an article from a national newspaper.
Assessment
1. Upheld
The ASA understood the term “modern stove” referred to stoves that complied with the provisions of Commission Regulation (EU) 2015/1185 (the Regulation), part of retained EU law, which set out the Ecodesign requirements for solid fuel local space heaters. The Regulation was aimed at reducing the environmental impact of such heaters. We considered consumers would understand the claim “modern stove and dry wood fuel can significantly lower emissions and improve efficiency compared to an open fire or older stove” as meaning that a modern stove, when used to burn dry wood fuel, would produce lower emissions, and be more heat efficient, than an open domestic fireplace or older stove burning the same fuel. They 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).
We assessed the evidence provided by the SIA. The letter from the Ministry of Housing Communities and Local Government stated the Ministry’s understanding that it was possible to significantly reduce the amount of smoke emitted through domestic burning if 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 consumers used an Ecodesign stove as an alternative to open fireplace or older stove. The guidance also stated that both open fireplaces and stoves were major contributors to PM2.5 pollution. While we acknowledged the guidance provided stated using Ecodesign stoves could produce less PM2.5 than modern stoves when burning wood, that only related to PM2.5 rather than other emissions.
The NAEI dataset and report categorised wood fuel under three headings – dry, seasoned, and wet. It provided data for, among other sources, ‘Domestic Closed Stove – Ecodesign’ and ‘Domestic Fireplace – Standard’. We considered the terms “modern stove” and “open fire” in the ad were shorthand for those categories. Aside from the Ecodesign, we considered the several other Domestic Closed Stove types set out in the data (Basic, Upgraded, and Advanced), all of which predated the Ecodesign stove, were covered by the shorthand “older stove” used in the ad. We therefore assessed the most recent data for GHG emissions and other pollutants, which was from 2023, in relation to burning dry wood in the older stove types, a modern stove, and an open fireplace.
The data showed modern stoves emitted significantly less PM2.5 than open fireplaces. However, it showed modern stoves emitted more PM2.5 than the older stove types listed. It showed a comparative decrease in some emissions, such as methane, nitrogen oxides, and black smoke. However, it also showed that other emissions were higher, and in some cases significantly higher, for dry wood burned in a modern stove as opposed to an open domestic fireplace, such as sulphur dioxide, carbon monoxide, and several other toxins. Between modern stoves and older stoves, the data showed increases in pollutants such as carbon monoxide, methane, and sulphur dioxide. The data therefore did not show a significant decrease in all relevant GHG and other air pollutant emissions between older stoves and open fireplaces, and Ecodesign stoves.
We next reviewed the independent report commissioned by SIA, and the report commissioned by Defra related to emissions factors for domestic solid fuels. The SIA report compared smoke, PM, methane, and carbon dioxide emissions for modern stoves with those from open fireplaces and older stove types. The study was conducted 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 levels of each pollutant than open fireplaces and older stoves. The Defra-commissioned report showed that a moisture content of between 10% and 20% was optimal for reducing emissions from wood burning. 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. We acknowledged SIA’s comments that they had intended the claim to relate to the findings in relation to PM2.5 and black smoke, and wood with a moisture content within the parameters set out in the Defra-commissioned report. However, that information had not been included in the ad. 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. Furthermore, the findings of the SIA-commissioned report related to a specific quantity of wood that had a specifically defined moisture content, which had not been demonstrated to be representative of how consumers were likely to use the stove type.
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”, as consumers were likely to understand it, had not been adequately substantiated.
On that point, the ad breached CAP Code (Edition 12) rules 3.1, 3.3 (Misleading advertising), 3.7 (Substantiation) and 11.1 (Environmental claims).
2. Upheld
The CAP Code stated that comparative environmental claims could be justified if the advertised product provided a total environmental benefit over that of competitor products and the basis of the comparison is clear.
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” 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 a “very low” level 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 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 World Health Organisation (WHO) recommended 24 hour exposure value. However, the review stated that according to the WHO there was no safe level of PM exposure. It further stated 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 as consumers were likely to understand it, had not been adequately substantiated.
On that point, the ad breached CAP Code (Edition 12) rules 3.1 (Misleading advertising), 3.7 (Substantiation), 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 future ads did not claim modern stoves emitted significantly lower emissions than open fireplaces or older stoves, nor that they were a very low emission way to heat the main living space of a home, without adequate substantiation. We also told them to make clear the basis of comparative environmental claims.
