Review of literature on residential firewood use, wood-smoke and air toxics

Technical Report No. 4
Environment Australia, June 2002
ISBN 0 6425 4868 4


1.1 This study

This literature review, initiated and funded by Environment Australia, consolidates the current state of knowledge on toxic emissions to the atmosphere from domestic firewood-burning appliances used in Australia. A thorough search for published information has been conducted and State and Commonwealth pollution control and energy authorities have been contacted seeking additional/unpublished material. The solid-fuel industry and other organisations with possible interests in wood-smoke emissions have also been approached for information. The main focus of the review is toxic compounds emitted by residential firewood use. General emission data, appliance technology, and ambient air measurements of wood-smoke support this focus.

In order to place the information on emissions into an appropriate context, the review has included information on government policy and regulation, standards, trends in residential firewood use, health impacts, and mitigation programs. Much of the recent discussion in Australia on the possible environmental risks associated with residential firewood combustion includes information from the international community. Thus, relevant material published in the international scientific and policy literature has also been reviewed.

This review of toxic emissions from woodheaters and open fireplaces will form part of a State of Knowledge Report on air toxics. This review supports the commissioned study Characterisation of Emissions from Domestic Solid Fuel Burning Appliances (Wood-heaters, Open Fireplaces). This research has been commissioned by the Minister for the Environment under the auspices of the Living Cities – Air Toxics Program.

1.1.1 Review Format

The literature review has been divided into two main sections, the first dealing with Australian literature and the second dealing with international literature. This distinction, while arbitrary in the scientific sense, is useful from an Australian perspective because it clearly identifies local expertise and interest, and provides a clear statement of the state of local knowledge. Effort has been made to ensure the Australian section is as comprehensive as possible. This has meant including some published reports, papers and articles that are essentially secondary sources, i.e. they do not contribute new scientific or policy information, although they do often provide a different interpretation or point of view on the primary information.

The international literature has been selected on the basis of its relevance to Australian issues or its importance to the international understanding of residential firewood combustion, wood-smoke and health impacts of wood-smoke.

The text within each section of the review provides a general discussion of the issues under consideration and selected quantitative data from the sources cited. Some interpretation of the published information is included, but it is not the aim of this review to critically examine all the information covered. Where opposing points of view are presented in the literature, these are highlighted.

The Harvard citation style has been adopted (author and year of publication cited in the text) and a full alphabetical list of all references is provided.

All quantities have been presented in metric units, with conversions applied if the original material is in other units. Conversion figures are given in the listing following the definitions and abbreviations. A common terminology has been used throughout, rather than using terms in the original publication. The most common change is to refer to wood-stoves (common US terminology) as woodheaters (see list of definitions).

Approximately 500 books, scientific papers and government/industry reports have been examined as part of this literature search, of these about 350 are cited in this review.

1.2 Background

Firewood use for residential heating declined for many years through the 1950s and 1960s in Australia, as more convenient fuels, such as heating oil, increased in popularity. In 1978 Australia adopted a policy of world-parity pricing for petroleum fuels and the price of heating oil increased rapidly. In regions without reticulated natural gas the cheapest alternative heating fuel was firewood (Todd 1981a).

In the United States and New Zealand, oil prices had increased some five years earlier and a new style of wood-burning domestic heater had developed. Thus, when the Australian public looked for alternatives to the oil-fuelled heater, there was a substantial overseas business in woodheaters already in existence. Imports, particularly from New Zealand increased very rapidly (Figure 1.1). It took five years or so for the Australian manufacturing industry to tool up and take a significant share of the local market. Firewood use grew rapidly between 1978 and about 1990, before reaching a peak in about 1992 or 1993 (see section 2.2 Residential wood-heating trends). A gradual decline has occurred since then.

The significance of the import figures to the discussion of air toxics is that cheap imported appliances from Taiwan dominated the period 1978 to 1982/3. These appliances were based on traditional designs, referred to in the United States emissions estimates as 'Conventional Pre-Phase 1 Wood Stoves' (US EPA 1996a). They were less efficient, produced more emissions and had relatively short working lives. It seems likely (although there is no data to support the supposition) that they were replaced with the second generation of woodheaters during the early 1980s.

The second-generation woodheaters, based largely on New Zealand designs, rapidly gained popularity and were the basis of the Australian industry (Todd 1996a). Most of the woodheaters now in use in Australia were installed after about 1984/85. Industry sources suggest woodheaters have a working life of 15 to 20 years. Thus, it is likely that this second generation of heaters is going to require replacement with new woodheaters or other types of domestic heating over the period 1999 to 2010. This is an important feature of the Australian domestic heating market, because it provides government with an opportunity of influencing householders in their choice of replacement heater over the next few years.

Figure 1.1: Imports of woodheaters into Australia, 1976 to 1985 and Australian manufacture of woodheaters 1977 to 1882 (when published data ceased).

Figure 1.1: Imports of woodheaters into Australia, 1976 to 1985 and Australian manufacture of woodheaters 1977 to 1882 (when published data ceased).

Source: Todd (1986a)

The present situation is summarised in Table 1.1. This shows that firewood is used in all states and territories. Victoria having the largest firewood use, followed by New South Wales. Queensland, South Australia, Western Australia and Tasmania each use around 0.4 to 0.5 million tonnes per year for residential heating. ACT and the Northern Territory have smaller demand.

The rapid change in preferred heating fuels in Australia was an unforeseen consequence of the decision to move to world-parity pricing for oil. For this reason there was little official response to the increase in the number of woodheater installations. However, within a few years it was apparent that the building regulations did not cater adequately for safe installation of woodheaters as a large number of house fires were occurring (see section 2.3 Policy and Standards). This serious safety issue prompted the Standards Association of Australia (now Standards Australia) to establish a committee to prepare installation standards for residential solid-fuel burning appliances (Committee CS/62). This committee prepared an installation standard (AS 2918) and went on to prepare standards for measuring appliance performance and emissions (see section 2.3).

Concerns about wood-smoke problems occurring in Australia were expressed as early as 1981 (Todd 1981b), but the general public did not perceive wood-smoke as a serious pollutant and so there was little official response. Through the 1980s, when growth in firewood use was at its greatest, the accepted ambient air guideline for PM10 concentration was 150µg/m³ (24 hour average). Even in cities with very high woodheater use and poor dispersion, such as Launceston, Tasmania, this guideline was only exceeded once or twice per year.

Table 1.1: Estimates of the number of households using firewood for as their main heat source and secondary heat source and estimates of total firewood use
Firewood using households 1999
State Main t/year Secondary t/year Total (t)  
NSW 351800 2 117267 1 820867  
Vic 240900 4.324 180675 1.932 1390716  
Qld 128700 2.9 32175 1 405405  
SA 107400 3 26850 1 349050  
WA 176400 2.53 44100 1 490392  
Tas 104700 4.8 12564 2.2 530201  
NT 1800 3 450 1 5850  
ACT 6700 3.7 5025 1.9 34338  
Australia 1118400   419106   4026818 firewood (t)
          1537506 houses (no.)

Sources: Number of households using firewood as main heat source (ABS 1999)
Number of households with secondary firewood use (adapted from Todd et al. 1989a)
Firewood use per household (adapted from Todd et al. 1989a)

However, epidemiological studies in USA and Europe were indicating that PM10, or respirable particles, might be a more serious health risk than previously thought (see section 3.5 Human Health). This raised community concerns and several community groups became active opponents of increased firewood use. With the publication of the Air NEPM (see section 2.3.1), setting an ambient air quality goal of 50µg/m³ for PM10, urgent action to deal with the wood-smoke problem was required. Cities like Launceston were experiencing 65 breaches of the goal per year. At the same time, concerns about the toxic nature of wood-smoke were receiving greater attention, further adding to the need to take action.

Meanwhile, an Australian woodheater manufacturing and retailing industry had developed along with a very dispersed firewood supply industry. In 1997, the Australian Wood Heating Association (now called the Australian Home Heating Association) estimated their industry was worth $200 million per year and employed 5500 (full-time equivalent) people (AWHA 1997). The capital invested by the 1.5 million households using firewood for heating is also significant. A new woodheater will cost around $1500 to $2000 installed, a masonry fireplace and chimney considerably more. On the assumption that current investment in this form of heating is worth about half the current replacement value, the Australian householders have $1 to 1.5 billion invested in wood heating. Thus, measures to control the wood-smoke problem must be considered in the light of economic and social issues as well as the environmental health issue (Todd 1988).

The literature reviewed in the following sections of this report provides the detail and background for ongoing wood-smoke management in Australia.

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