Evaluation of the effects of PM2.5 due to domestic solid fuel burning on health outcomes in Scotland

5 Selection of policy options for assessment

5.1 Policy context

The control of domestic solid fuel emissions has a long history in the UK, with the current phase starting in 1956 with the passage of the first Clean Air Act. This mandated the creation of Smoke Control Areas (SCAs) where the emission of smoke from chimneys was banned and only approved solid fuel could be used, other than in “exempted appliances”. This list of appliances, which has become known as the “Defra approved” list, includes many multi-fuel and log burning appliances, thus creating a loophole which allows solid fuel use within SCAs and makes them very hard to enforce. The original legislation was accompanied by a grant scheme which allowed households to upgrade their solid fuel appliances to gas or electricity. At the time, this represented a major shift away from reliance on solid fuel for heating and towards gas or electrical central heating. In the UK, there is only a small proportion of households who rely on solid fuel for heating, almost all of whom are in rural areas. The proportion is higher in Scotland, with around half of those who are reliant on mineral fuels being considered fuel poor^[28].

Since the 1950s and 60s, air pollution control has tended to focus on industry and transport as the main emission sources. The last iteration of the Clean Air Act was 1993, although it was amended and the enforcement procedure updated in England by the Environment Act 2021. Nevertheless, it remains unclear how enforceable the provisions of the Clean Air Acts are in a modern context, with a media report showing just 24 fines and no prosecutions by English LAs despite over 15,000 complaints^[29]. Interviews with Local Authority officers in connection with the evaluation of the English Domestic Solid Fuels Regulations revealed a similar level of pessimism over the enforceability of the fuel quality standards it imposed.

Focus on domestic solid fuel use as a key source of air pollution has re-emerged in recent years, as a result of successful controls on transport and industrial emissions and a rise in the installation of solid fuel appliances as secondary heating sources. This has been facilitated by the drive towards increased renewable heat in both the UK and EU, although many respondents in the recent Ipsos survey of national burning practices revealed cost (e.g. to supplement central heating) and aesthetics as the primary reasons for burning.

In many EU Member States, reliance on wood, in particular, as a heating source is generally more prevalent than in the UK. This has resulted in the inclusion of air pollution emission standards for small space heating appliances within the mandatory Eco-Design standards. The current standards are also applicable in the UK, as retained EU law, but a Defra study (Emission Factors for Domestic Solid Fuel, EFDSF^[30]) found that Eco-Design emissions were no lower than those from earlier stoves (albeit noting significant uncertainties involved due to the small sample size)^[31]. Furthermore, the current revisions to Eco-Design currently underway in the EU will not necessarily be adopted in the UK. Many EU Member States have gone considerably further than the Eco-Design standards, with their own, national standards (such as Blue Angel in Germany, Nordic Swan in Sweden and Green Flame in France) which, while not mandatory, are incentivised through policy measures. A strong focus on modernising the stock of domestic appliances in several countries has resulted in the mitigation of air pollution emissions and has facilitated the development of both cleaner appliances, such as automatic pellet fed boilers for residential use, and abatement technologies, such as ceramic filters to reduce PM emissions. Neither are common in the UK.

Two further areas for control have been explored in UK policy, although both are currently in relatively early stages. The Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020 banned the sale of house coal in England, as well as restricting the supply of unseasoned wood and reducing the permitted sulphur content of manufactured solid fuels. An evaluation of the regulations, undertaken by Ipsos and AQC/Logika, revealed that while compliance with the regulations was relatively good in the formal supply chain, informal and grey market supplies have been largely unchanged (in the short term) and that the enforcement regime is weak, relying on Trading Standards Officers, whose scarce resources tend to be prioritised elsewhere.

The second area is that of planning and development management. There are conflicting drivers and messaging in this area, with policy largely driven by climate and zero carbon concerns. For example, the 2023 consultation on the Future Homes and Buildings Standards [for England] stated that the standards are “unlikely to allow the installation of biofuel systems, including wood and manufactured solid fuels”^[32]. Airtightness standards are also likely to mean that functional chimneys are not allowed in new homes. However, as noted in Cleaner Air for Scotland 2, “flues…which form part of a domestic biomass system have permitted development rights (PDR)” which means that LAs have little or no control over their installation.

Overall, this represents a patchy policy landscape with respect to domestic solid fuel use, combining very old legislative measures, designed when the heating profile of UK homes was very different, with more recent but often unenforceable measures around fuel and buildings. This does not represent a coherent policy package comparable to, for example, controls on road transport emissions (comprehensive and tightening vehicle emission standards and tax incentives for cleaner fuels) or integrated pollution control for industry. While this is also true of many EU Member States, there are a variety of measures that can and have been used in other countries and the experience with which could inform policy in Scotland.

5.2 Defining a long-list of policy options

The project team has undertaken a review of available literature on potential measures to address emissions from domestic solid fuel use. Measures aimed at external burning (e.g. bonfires or barbeques) or non-domestic scale appliances (medium combustion plant, commercial boilers, etc.) have been excluded. The review drew heavily on previous work by the AQC/Logika and partners for the European Commission^[33]. This included the development of a database of around 120 measures adopted by Member States, regions or cities to address the impacts of domestic solid fuel use (mainly wood burning) on air quality. Through this work, a basic nomenclature of measures was developed:

• Operational measures: These measures focus on how solid fuel appliances are used, relating to operational aspects such as maintenance procedures applied and the quality of fuel used. Such measures can include operational training for users (mandatory or voluntary), maintenance requirements (such as the need to use registered chimney sweeps, and the frequency of inspections), and the regulation of fuel either sold or used, such as a requirement to only sell seasoned wood.
• Stock renewal: Initiatives to replace older, more polluting solid fuel appliances with cleaner bioenergy technologies or alternative technologies. Such measures include incentivising the sale of cleaner operating stock, stove or boiler swap-out schemes (voluntary or mandatory), or incentives for other heating technologies, such as air-source heat pumps or solar PV.
• Restricting use: Measures aiming to prevent the use of solid fuel appliances altogether. These are typically limited in geographical or temporal scope (or both).
• Public information: Initiatives to encourage beneficial behaviours as regards solid fuel use or use of non-solid fuel alternatives (including non-combustion). Campaigns could be aimed at the general public, but they could also be sector specific, such as the hospitality trade or fuel retailers, and could focus also on health impacts of solid fuel burning.

There were also two basic policy aims identified: (1) “burn better” by improving the emission performance of domestic burning; and (2) “burn less” by reducing the frequency of burning and/or numbers of households burning. The work concluded that successful policy packages are likely to contain measures from each category and allow the balance between “burn better” and “burn less” to shift, depending on location and the availability of alternative heating options. There will also need to be an integration across governance levels, i.e. from national to local, with clear policy aims for each. The following subsections outline possible policy measures for Scotland, using the nomenclature described above.

5.2.1 Operational

Fuel quality standards and fuel restrictions or incentives: Mandatory specifications for solid fuels, including limits on moisture content, ash, sulphur, nitrogen and chlorine, certification requirements (e.g. ISO standards), and bans on particularly polluting fuels. This could include, e.g., Taxation of solid fuel burning: Alignment of taxes on wood and solid fuel burning with other heat sources, or direct taxation of particulate emissions to reflect health costs and discourage polluting behaviour.

Inspection, testing and enforcement regimes: Regular compulsory inspections of stoves, boilers and chimneys by authorised professionals, including on-site emission measurements, fuel checks, and enforcement actions such as fines or forced shutdowns for non-compliance.

Certification and training of professionals: Voluntary or mandatory certification schemes and training programmes for installers, chimney sweeps and sales staff to ensure correct installation, operation and consumer advice.

Voluntary schemes, labels and quality marks: Non-mandatory eco-labels, quality marks and voluntary certification for appliances and fuels that exceed regulatory requirements, used to steer markets and consumer choice.

5.2.2 Stock renewal

Emission and efficiency standards for appliances: Mandatory limits on particulate matter (PM), carbon monoxide (CO), organic gaseous carbon (OGC), NO_X and minimum energy efficiency requirements for solid fuel stoves and boilers, often aligned with EU Ecodesign or national standards and applied at market entry or installation stage.

Appliance classification and labelling schemes: Star-rating or class-based systems that categorise stoves and boilers according to emissions and efficiency performance, used to regulate market access, inform consumers, and determine eligibility for subsidies or restrictions.

Phase-out and replacement of high-emitting appliances: Legal requirements or deadlines to retrofit, replace or decommission older, inefficient or non-compliant stoves and boilers, often linked to the appliance’s age, emission class or test results. This can also be tied to changes in home ownership.

Financial incentives for appliance replacement and upgrades: Subsidies, grants, tax deductions or scrappage schemes supporting replacement of old solid fuel appliances with low-emission models, alternative heating systems (e.g. heat pumps), or cleaner fuels.

Conditional subsidies linked to performance: Public funding conditional on meeting specific emission classes, fuel certification, eco-labels or ultra-low emission thresholds, sometimes with performance-based bonus components.

Research, development and transitional technologies: Public funding for R&D to integrate emission-reduction technologies into solid fuel appliances, particularly to provide lower-cost transitional options for low-income households

5.2.3 Restricting use

Restrictions on installation of solid fuel appliances: Limits or bans on installing new solid fuel heating appliances in specific areas (e.g. urban centres, high-pollution zones, new buildings, or buildings without chimneys), sometimes combined with planning consent requirements. E.g. Restrictions on flues and permitted development rights: Removal or amendment of permitted development rights for flues, particularly within Smoke Control Areas, to limit uncontrolled installation of solid fuel appliances.

Operational restrictions and temporary bans: Rules limiting when and how solid fuel appliances may be used, including temporary bans during air pollution episodes, weather-based “burning alerts”, seasonal restrictions, or limits on frequency of use. E.g. Ban on secondary or non-essential burning: Prohibition of solid fuel burning where it is not the primary source of heating, to reduce discretionary and high-emission use.

Local authority powers and zoning approaches: Delegation of powers to municipalities to regulate solid fuel burning locally, including bans, stricter standards, differentiated rules by zone, or additional consent requirements, e.g.: a low emission zone approach which incorporates domestic burning.

Smoke Control Areas (SCAs): Designation or expansion of Smoke Control Areas to restrict the use of polluting solid fuels and appliances, including extending SCA rules to non-standard dwellings such as moored residential boats. In the EU, restrictions on domestic burning have also been introduced as part of Low Emission Zones.

Local monitoring, enforcement and complaints handling: Active investigation of non-compliance, monitoring of domestic burning hotspots, inspections of fuel retailers, and enforcement of smoke control and fuel regulations.

Targeted measures for high-pollution areas: Stricter standards, bans or incentive schemes focused on cities, valleys or regions with persistent PM exceedances attributable to residential solid fuel combustion.

5.2.4 Information

Public information and awareness campaigns: National or local campaigns informing households about the health and air-quality impacts of solid fuel burning and promoting cleaner practices, appliance choices and fuel use.

User behaviour and best-practice guidance: Guidance, training and tools aimed at households to improve combustion practices (e.g. ignition techniques, fuel storage, air supply management), recognising user behaviour as a key emission driver.

Energy advice and household support services: Deployment of energy advice officers and local support services to help households reduce energy demand, switch fuels, and access available grants or retrofit programmes.

Digital tools and platforms: Online platforms, apps and self-reporting tools to support monitoring, user awareness, self-evaluation of practices, and dissemination of guidance and regulatory information.

5.3 Screening of options and selection of shortlist for modelling

A multi-criteria analysis approach has been undertaken for the long list , to assess the best fit between the potential measures and Scottish Government’s desired outcomes. The criteria used are presented in the following table. The policy options and scoring criteria were loaded into a spreadsheet tool, and moderated/sense checked by the project team. The tables below show the criteria used for the analysis, and following, the final list of policy options including RAG ratings. The policy options were scored against the criteria by the study team and members of the Steering Group using a simple 0-3 score, with 3 always being positive. As an example, for impacts on air quality, the greatest reductions in emissions and/ or concentrations would score a 3, with 0 being negligible or no impact on air quality, however in relation to costs, 0 would represent the highest cost, with 3 representing the least or no cost. Scores were then averaged across scorers and the averages summed for each of the three criteria groups (impact, cost and availability). Policy scenarios were then developed based on overall highest scores, and separately highest impact and lowest cost. There were no weightings applied to the scores, which meant that impact (with 4 criteria) carried slightly more weight in the overall scoring than cost or availability. The final outcomes scores are shown in Table 5‑2.

5.4 Modelled policy scenarios

Following an analysis of the scores, three high-level policy scenarios were devised using the multi-criteria analysis as a guide rather than a strict prescription. Note that they are not an analysis of the specific features of any one policy measure – this would be beyond the scope of this project – but they provide an indication of the potential impact of the different policy types. The three scenarios are:

1. Burn less: The main component of this scenario is a nation-wide information campaign, aimed at both better use of appliances and the selection of correct fuels, and an increasing awareness of impacts on health.

2. Burn better: This scenario focusses on the regulation of fuels as well as an information campaign on the selection of correct fuels. It includes a campaign of mandatory chimney sweeping and appliance inspection, which has proved effective at eliminating “wet” wood burning in Germany^[34].

3. Targeted stock upgrades: In this scenario, a program of upgrading fireplaces and stoves is implemented in the six Local Authorities most impacted by solid fuel emissions. The precise upgrade mechanism has not been defined, but could include one or both of mandatory measures or means-tested financial support.

The modelling assumptions for each of these scenarios are set out in the next section.