Woodheaters and Open Fireplaces

History

A woodheater is a domestic spaceheater with an enclosed combustion chamber which is used to control the amount of air entering the fire. Some appliances are fitted with water heating coils and some can be used for basic cooking tasks. Slow combustion cooking stoves are not dealt with in detail in these notes, although many of the same principles apply. For legislative purposes a cooking stove is defined as having a hot plate and an oven of at least 28 litres capacity. Some cooking stoves provide hot water for central heating in water filled radiators.
An open fireplace is either a masonry (brick, stone or concrete) chimney with an open fronted combustion area, or a metal, prefabricated appliance with an open front. Some open fireplaces are fitted with air circulation ducts around the fire to improve efficiency.

In Europe and North America, large populations (which put more pressure on firewood supplies) and cold climates meant that the poor efficiency of the open fireplace was inadequate so more efficient controlled combustion heaters were developed. These included the cast iron, freestanding appliances, such as the Franklin stove and the ornate European tile stoves or Kachelofens (see Figure 1). A variety of traditional woodstove designs can be found at Temp-Cast Masonry Heaters. The Kachelofen, first used in the 14th century, is still a very effective design. It allows a wood fire to burn rapidly and at high temperatures. These features (as discussed in more detail below) lead to efficient and clean combustion. The heat released is stored in the brick and tile of the heater, which can weigh a tonne or more, and slowly released into the living space over many hours. Modern Kachelofens are still being installed in European and North American homes, but very few have found their way to Australia.

Figure 1 A ceramic Kachelofen woodfired heater (courtesy of the Masonry Heater Association of North America).

There was little technical development of woodheaters during the 1900s until the rapid rise of oil prices in 1973 prompted the worldwide search for alternative energy supplies, and the woodheater was rediscovered. One important development occurred in the South Island of New Zealand, when a local farmer designed a woodheater with an air supply that entered the firebox above the door, rather than at the bottom or under a grate. This design feature meant that it was possible to maintain a flow of clean air down the inside of a glass panel in the door, keeping the glass clean and the fire visible (Figure 2). The design was bought by Kent Heaters in New Zealand, which for a short period became one of the largest woodheater manufacturers in the world. Other manufacturers quickly adopted this design feature and now it is the standard for all heaters with glass doors.

Figure 2 Schematic of woodheater.

Our indigenous oil supplies meant that Australia was sheltered from oil price rises until 1978, when oil prices in Australia rose quickly. From 1978 to about 1990, woodheaters experienced a rapid increase in popularity. In the early 1990s, however, concerns over woodsmoke and a preference for more convenient heating appliances triggered a gradual decline in the number of households choosing to heat with wood. This coincided with large marketing campaigns by gas and electricity heater manufacturers, and the reduced costs of heat pumps. Figure 3 shows the declining trend in popularity of firewood for space heating in Australia from the 1950s to 2000. The numbers shown prior to 1975 are uncertain and the projections from 2000 reflects the trends in 2000, and is a 'best guess' of future use.

Figure 3 Firewood use over time in Australia.

Modern Woodheater Design

Modern woodheaters are relatively sophisticated appliances. In Australia, two types of appliance have proved most popular: the free standing room heater and the fireplace insert heater. Open fireplaces are discussed separately below. Much less common (but commercially available) are woodfired central heating furnaces and 'zero clearance' woodheaters (which can be built into the wooden frame of the house). In North America and Northern Europe, domestic woodheaters fueled with wood pellets or woodchips are popular, but these appliances have not been marketed in Australia to date.

Woodheaters compete with other types of domestic space heaters: electric, natural gas, LPG, and oil. The features of woodheaters, promoted by woodheater retailers are their appearance, their high heat output and their low running costs (see economics section below). Appearance/style is a matter of individual preference, although there seems to be an almost universal appeal of watching the flame of a wood fire. Woodheaters with large glass doors are popular and new designs include 'bay window' doors. It is interesting that the early woodheater designs tried to copy oil heater styles because oil heating was very popular in the 1960s. The woodheaters then developed into a style of their own. Now, some modern gas heaters replicate woodheaters, even to the point of having simulated logs and burning embers.

Figure 4 A modern woodheater with large glass doors (courtesy of Hearthhouse)

Hundreds of different models of woodheater are available on the Australian market. Table 1 summarises their main performance features.

Performance characteristic	Typical values	Comments

Maximum heat output	12 to 20 kW	A few models have maximum heat outputs up to 30 kW
Minimum heat output	2 to 5 kW	Small fuel loads can be used to achieve lower heat outputs
Burn time on single load	4 to 12 hours	Most manufacturers try to achieve overnight burn capacity of 8 hours
Smoke emissions	1 to 5.5 g/kg	Wood-smoke emissions are discussed in detail below

Table 1 Performance characteristics of modern woodheaters.

Even though woodheaters sold in Australia are 'room heaters', their high heat outputs mean that a whole house can be heated by leaving doors to rooms open, or by ducting hot air to other parts of the house. This feature of woodheaters has contributed strongly to their popularity.
Some design features that improve the performance and reduce smoke emissions include:

Pre-heated combustion air to prevent 'flame quenching' (cold air will extinguish the edge of a flame, increasing pollution and decreasing efficiency);

Maintaining hot inside surfaces in the combustion chamber to prevent flame quenching (as a flame approaches a cold surface the gas temperature will drop and the flame will go out);

Designing the air supply and combustion chamber so as to maximise turbulence, and thereby ensure good mixing of gases from the wood and air (oxygen for combustion);

Ensuring that the heat exchange is efficient enough to recover most of the heat from the flue gas, but not cooling the flue gas to the point where the natural draught drops too low and the fire does not 'draw' (the hot flue gas causes a pressure drop which sucks in new combustion air); and

A fixed minimum combustion air supply so that the fire cannot be totally 'starved' of air (insufficient air causes high emissions of smoke).

Wood-Smoke

In recent years there has been a lot of attention paid to airborne fine particles less than 2.5 microns (millionths of a metre or mm) in diameter. These very small particles are able to penetrate deep into the lungs, while larger particles in the air are trapped in the nose or throat. Even in 'clean' air, we breathe millions of fine particles into and out of our lungs in the 10,000 litres of air that pass through them each day. In polluted air, the normal cleansing functions of the lungs become overloaded leading to health problems linked to the number and chemical composition of the fine particles.

Several overseas studies undertaken in recent years have indicated that for each 10mg/m³ increase in fine particles (PM10, averaged over 24 hours) in outdoor air, there is a 1% (±0.5%) increase in mortality (e.g. Schwartz 1993, Vedal 1997). Epidemiological studies suggest that the chemical composition of the particles is not a critical factor, and that it is simply the mass of these fine particles in the air that causes problems. These findings have far reaching implications for air pollution control. The situation is complex, with considerable variation in findings from one study to the next, and some experts feel that there may be more to the problem than simply the concentration of fine particles (Vedal 1997).

Despite the uncertainty, these studies have important significance for pollution control, and there are likely to be much stricter controls imposed on fine particle concentrations in the air. For example, the current Australian national standard for fine particles in ambient air (PM10) is 50 µg/m³. This is a significant reduction from the previous 'guideline' of 120 µg/m³ (Todd 2003). Also, the much smaller particle size (PM2.5) maximum exposure standards are 25 µg/m³ (Environmental Protection and Heritage Council 2006).

Current knowledge suggests that the fine particles in wood-smoke are the main reason woodheaters need to be controlled. But woodheaters also emit carbon monoxide (CO). At low concentrations (10 to 50 parts per million (ppm)), CO causes headaches and decreases reaction times. It can also cause angina and impair vision. At higher concentrations (300 to 500 ppm), CO can cause coma and death. Being odourless and colourless, people may not be aware that they are exposed to CO, which makes it more difficult to control. Motor vehicles and woodheaters are significant suburban sources of CO. It is unclear, however, to what extent woodheaters are contributing to unacceptable CO levels as each individual wood heater and fuel used produces a different CO output at different times in combustion. The current Australian standard for maximum CO exposure is 9 ppm (Environmental Protection and Heritage Council 2006).

Standards for Woodheater Emissions

An Australian Standard was developed as a first step towards controlling emissions of fine particles from woodheaters. The standard was published in 1992 after four years of development, but it was not until 1993 in Tasmania that the standard was first called up in any state pollution control legislation (i.e. until that time the 'Standard' was voluntary). ACT followed suit in 1994 and NSW in 1996. Western Australia introduced a new law in 1998, requiring all heaters sold in the State (either new or second-hand) to comply with the emission standard. The Australian/New Zealand Standard, AS/NZS 4013 is now used to regulate the maximum particle emission rates in most states and territories within Australia. The Australian Standard for the installation of woodheaters (AS/NZS 2918): Domestic solid fuel burning appliances - Installation) was developed to control the installation of woodheaters. The woodheater resource handbook (HB 170): Wood Heating Resource Handbook Guide to the Selection, Installation and Operation of Wood Heaters) has been published to assist the implementation of this Standard.

In response to increased public health concerns and developments in cleaner burning heaters, the Australian Standards committee in 1999 decided to change the allowable emission standard for new heaters from 5.5g/kg to 4g/kg. This 25% reduction in allowable emissions meant that woodheater manufacturers had to redesign their products to meet the tougher standard. Also, in recognition of the need to continue better characterising woodheater emissions from models actually sold to the public, a National Woodheater Audit Program was implemented with funding from Commonwealth, NSW, Victorian, Western Australian and Tasmanian environment agencies. Retail models representing popular Australian models were purchased from retailers and tested for emissions performance. The National Woodheater Audit Program report released by the Department of the Environment and Heritage in May 2004 demonstrated the extent to which the extent of wood heaters failed to comply with standards, in terms of emissions performance (58%), engineering design specifications (55%), and labeling requirements (72%)(DEH, 2004). Findings from this program point to reviewing the system of certification, and increased measures to improve compliance (for more information (pdf) click here).

Correct Woodheater Operation

Taking care when operating woodheaters is one of the most significant things householders can do to help protect the environment. A well operated woodheater will produce only half as much smoke as one operated poorly, and a very badly operated heater may produce ten times as much smoke. The well operated heater will also produce more heat from each piece of wood burnt. If everyone with a woodheater used it properly, there would be significant reductions in winter haze and a subsequent improvement in community health. The difficulty has been to inform all woodheater owners on how to burn their fires cleanly, and then encourage them to always 'do the right thing'. A number of community education programs have been initiated, and more are planned.

The following suggestions on using woodheaters cleanly include brief explanations of why each suggestion can be effective. Each model of woodheater will have slightly different operating characteristics. It is therefore important for woodheater owners to understand the most effective operating hints that are applicable for their particular case.

Woodheaters should always be on high burn rate (air controls fully open) for 20 to 25 minutes after reloading. Once the fire is well established, air controls can be adjusted. This is one of the most important aspects of correct heater operation. When a new load of wood is added, the wood is cold and contains some moisture. It is essential to reheat the firebox and dry the wood so that good combustion can occur. All woodheaters will smoke briefly during this warm-up period because some of the volatile gases are escaping unburnt. In heaters that comply with the Australian standard, all visible smoke should cease once the heater is burning well. In older models of heater, only a faint smoke should be visible once the heater is operating well.

Do not over fill the heater. There must be enough space for the air to move down the glass and into the base of the fire, this means at least 5 to 10 cm between the front of the logs and the door. It is therefore important to make sure firewood is cut to the appropriate length for the heater. If the incoming combustion air cannot reach the base of the fire it cannot contribute to the combustion process and severe smoking can occur.

There must also be space above the top of the fuel load (between the firewood and the baffle plate) to allow flame to develop and burn off the gases released from the wood. If the whole firebox is crammed with wood the gases released from the wood pass directly into the cooler 'secondary combustion zone' above the baffle before they mix with air. Despite the term 'secondary combustion zone' the gases will not burn here unless they have been ignited in the much hotter firebox region of the heater.

If the fuel load has burnt down to a very low level so that there are only a few glowing coals left, it is important to add a bit of newspaper and some kindling when refueling so that there is a vigorous fire established quickly. It is possible for a new load of wood to smoulder for hours (literally) without any flame developing. This causes large releases of smoke. If flames are encouraged through use of paper and kindling, they will usually cause the new wood load to ignite effectively and reduce smoke.

When lighting a cold heater, always use sufficient dry kindling to establish a good fire quickly. It is also a good idea to put two or three loosely crumpled sheets of newspaper on the top of the fuel load when first lighting the heater because this burns rapidly, heats the flue and gets the draught going. Getting the heater and flue warmed up quickly is important in reducing smoke emissions.

Smaller logs should be used to get the fire established and for high heat output, larger logs are suitable for slower burning. Smaller logs have a higher ratio of surface area to volume. This means that the wood heats more quickly and the chemical reactions that release the energy stored in the wood take place faster.

Dry firewood should always be used. Wet wood means less efficiency and much more smoke. The energy required to evaporate the water in wet wood leads to lower temperatures and less complete combustion. Firewood should be stored in a well ventilated shed or other covered area. Firewood should never be stored against the wall of a house because it can provide a 'bridge' for ants, termites and other insects.

Logs should be placed in the firebox so that there is at least two centimetres between each log. This allows air to get into the hot area of the fire and leads to better combustion.

It is very important to check the heater flue for smoke every now and then. If it is producing lots of visible smoke for more than 15 minutes or so after lighting or refueling then you need to adjust the fuel to get a better fire. Each model of heater will have certain ways of loading the fuel that gives the cleanest burning. You will have to use trial and error to get the best arrangement for your heater.

Keep your heater and flue in good working order. The flue should be checked each year and cleaned of creosote if necessary. Partially blocked flues reduce airflow through the fire and lead to lower temperatures and more smoke.

If smoke from your heater is blowing into a neighbour's home this can be very annoying for the neighbour. If it is a regular problem it may be possible to solve it by increasing the height of your flue. But make sure the heater is correctly installed because a taller flue usually means the heater will run a bit hotter. If problems persist, assistance can be obtained from the pollution control authorities or members of the Australian Home Heating Association.

One of the attractive features of modern woodheaters is their ability to burn unattended overnight. This provides a warm home in the morning and means the fire does not have to be relit. But overnight burning is one of the major causes of excessive smoke. It is possible to burn some heaters very cleanly overnight, but this requires special attention to correct operation. In order to achieve a slow burn rate in a controlled combustion woodheater, it is necessary to reduce the supply of combustion air (i.e. starve the fire of oxygen) in order to cool the fire down and slow the release of gas from the wood. When the air is first reduced there will be some smoke produced because the still hot fire will be releasing more gas than could be burnt with the available air. If the air supply has not been turned down too far, a new set of combustion conditions will be established where the gas released from the wood is again in balance with the combustion air. The fire will burn cleanly but at a slower rate than with full air supply. But if the air supply is reduced too much, the fire will cool to the point where the flame disappears and it is no longer possible to maintain clean burning conditions. The key to clean burning under reduced air supply is to have a decent visible flame in the firebox (a little flicker of flame between two logs is not sufficient).

In practice, woodheaters that carry the Australian Standards (AS4013) certification (indicated by a label fixed to the back of the heater) are designed to ensure that there is always sufficient air to keep the flame, even when turned off as much as possible. In this case it is assumed that people are still operating their heater in accordance with operating instructions. That is, they are burning the heater on a high setting for 15 to 20 minutes after refueling (i.e. burning the fire brightly). If this is not done the firebox and new fuel load may never get hot enough to keep the flame present and even the new models of heater will smoke.

For heaters that do not carry the Australian Standards (AS4013) certification, it is possible (even easy) to reduce the combustion air to the point where the flame will disappear and the fire will smoulder for hours, producing unacceptable quantities of smoke. If the homeowner is careful with these uncertified heater models, it is still possible to use them so the wood burns reasonably cleanly, provided care is taken to never turn the air control so low that the flame disappears. It may take 10 to 15 minutes for the flame to disappear, so this requires a conscious effort to check the fire after reducing the air supply. Once a suitable minimum air control setting has been found, it should only require occasional checking. It is important for the homeowner to be aware that this might mean that their heater will no longer burn overnight. If this is the case, and they want to burn overnight, they should invest in a new model heater designed for clean overnight burning.

Even if uncertified heaters are used sensibly (i.e. not excessively starved of air) they will produce more smoke than the Australian Standards certified heaters. The heaters designed for cleaner burning usually incorporate many features aimed at reducing smoke, not only a fixed minimum air supply.

Open Fireplaces

Most homes in the southern parts of Australia built before 1960 had at least one open fireplace for heating. A typical masonry fireplace, however, only transfers 5 to 10% of the energy in the firewood into the living space, and the open fireplace lost favour because of this low efficiency and inconvenience. The main reason for this low efficiency is the large volume of air that is drawn out of the room and up the chimney. An open fireplace may draw 50 times more air than it needs for combustion up the chimney, or around 1000 m³/h. This means that all of the air in a modest sized living room is drawn up the chimney each 5 minutes, with cool air from outside replacing the room air.

Lack of turbulence in the combustion zone and flame quenching due to the relatively cool combustion air means that open fireplaces have relatively high smoke emission factors. Testing in the USA has shown emission factors of 17.5 g/kg of wood burnt (compared to an average emission factor of 3 g/kg for a correctly operated modern woodheater). The performance of open fireplaces can be improved by using heat recovery systems before the hot gas passes through the chimney. Such modifications can improve efficiency to 20-25%, a significant improvement, but still less than enclosed woodheaters. Careful operation of an open fireplace can reduce smoke emissions. Most important is to avoid a smouldering fire with little flame.

Safety

Any appliance in the living room of a home that operates with temperatures up to 1000°C presents potential safety risks. For woodheaters, the risks fall into two categories: house fires from incorrectly installed or maintained heaters and flues; and accidental burns caused by touching hot surfaces. Woodheaters and flues are designed to operate perfectly safely. However, problems can occur if the appliance is not installed correctly, i.e. if it is not installed in accordance with Australian Standard AS2918. This standard sets minimum clearances from walls and ceilings and minimum requirements for floor protectors. Studies of fire incident reports show that the area where the flue from a free-standing fireplace passes through the ceiling can be a problem if the flue is incorrectly installed and a flue fire occurs. A flue fire is the rapid burning of creosote that has accumulated in the flue. Flue temperatures can reach 1200°C and so proper heat shielding of combustible materials nearby is essential.

Figure 5 Woodheater safety.

Young children are most at risk from accidental burns. Children under two years old are attracted to the visible flame and reach out to touch it. Children between two and four are at risk of falling onto a heater while playing. Fire or safety screens around heaters should be in place when young children are present. Care must be taken with open fireplaces to ensure that burning logs cannot roll out and sparks cannot fall on to readily flammable materials. In addition the smoke from poorly drawing open fireplaces can cause unacceptable levels of indoor air pollution. Proper installation and sensible use of woodheaters and open fireplaces will reduce safety hazards to very low levels.

Economics of Heating Systems

Choice of a domestic heating system is not simply a matter of cost, but running and appliance costs usually influence the decision. One aspect that has made woodheaters popular is their relatively low running cost. Table 2 compares the running cost of different types of heating appliances for Perth. Small differences in the cost of 'useful energy' shown in the table should be ignored, because fuel prices and appliance efficiency can vary sufficiently to change the relative costs. The table shows that wood heating, gas heating and heating with an electric heat pump have similar running costs.

But this is only part of the picture. The capital cost of a woodheater (including installation) is usually in the range $1000 to $3000. If $1800 is taken as 'typical' and the expected life of the appliance is 15 years, the annual capital cost is $120/year. (Note that you can use many different methods for determining 'net present value'. They all depend on predicting future inflation rates and interest rates. Such predictions are virtually impossible over periods as long as 15 years.) If about 3 tonnes of firewood are burnt per year the total cost is about $480 per year.

Energy supply	Price (2006)	Energy content	Efficiency of use*	cents/MJ useful energy
Firewood	$120/t delivered**	16 MJ/kg	60%	1.25
Natural gas	7.65 cents /unit***	1 unit = 3.6 MJ	70%	3.03
Electricity (peak)	18.38 c/kWh ****	3.6 MJ/kWh	100%	5.10
Electricity (off-peak)	5.96 c/kWh ****	3.6 MJ/kWh	100%	1.65
Heat pump (peak)	18.38 c/kWh****	3.6 MJ/kWh	250%	2.04
Oil/kerosene	100c/L delivered	36.9 MJ/L	70%	3.87

Table 2 Running costs of various heating options for Perth based on February 2007 fuel/electricity costs.

*      These are approximate efficiencies only, different models of appliance will have slightly different efficiencies.
**    Firewood price shows considerable variation from $80 to $200/t, depending on whether its delivered, its quality and the local market.
*** Natural gas is charged at 7.65 c/unit for the first 100 units used on average per day, and 6.09 c/unit for over 100 units used on average per day.
        There is a 10.45 c/day supply charge (not included in above calculation).
**** These figures are based on the Synergy A1 tariff. There is also a 25.57 c/day supply charge for electricity (not included in above calculation).

The running costs in Table 2 have been calculated as follows:

The fuel/electricity cost is obtained from the supplier.

The cost is converted to a standard unit - the megajoule (MJ). This is done by dividing the cost of the fuel/electricity by the number of MJ in each unit of fuel/electricity. For example, if firewood costs $150/tonne this is equivalent to 15000 cents per 1000 kg or 15 c/kg. One kg of air dried firewood contains 16 MJ of energy, so 1 MJ costs: 15/16 = 0.9375 cents.

The cost per MJ is then divided by the efficiency (in percent) and multiplied by 100. For example, if the firewood is burnt in a heater with an efficiency of 65% the cost of useful heat is 0.9375 ¸65 x 100 = 1.44 c/MJ.

There is sometimes confusion over efficiency and running cost. An electric heater (excluding heat pumps/reverse cycle air conditioners) is more efficient than a woodheater, but it has a higher running cost. Thus, the notion of efficiency is not useful in comparing appliances that use different fuels. But if two woodheaters are compared, the one with the highest efficiency will have the lowest running cost.

The Woodheater Industry in Australia

(This section of the information file is based on estimates prepared by the Australian Home Heating Association).
The wood heating and firewood industries have a number of components. There are several major woodheater manufacturers in Australia and many small manufacturers. The estimated sales of woodheaters in Australia are around 40 000 units per year. This is a substantial drop from peak sales in the early 1990s. There are specialist flue manufacturers and manufacturers of hearths and heater accessories. There are several distributors that wholesale Australian and imported heaters. There is an extensive retail sector consisting of specialist woodheater retail outlets, specialist domestic heating outlets (wood, gas, electricity), hardware stores selling woodheaters and some major retail chains. There are heater installers and chimney sweeps. These sectors of the industry directly employ about 1000 people in Australia. The industry turnover at present is about $30 million per year (DEH, 2002).

The manufacturing sector requires a mix of skilled and unskilled labour. A significant proportion of manufacturing is carried out in rural towns where unemployment is often high. Retail and servicing is distributed through both urban areas and rural towns, providing jobs in areas of low employment. The firewood supply sector provides opportunities for farmers to supplement income through firewood royalties or cutting and delivering firewood themselves.

The domestic sector consumes about 4 million tonnes of firewood each year. About half of this is collected by householders for their own use and about half is purchased from commercial suppliers. Assuming an average purchase price of $100/tonne (higher in major urban areas, lower in rural areas), this industry is worth $200 million per year and creates employment for thousands of people, especially in rural areas.

The Future

Woodheaters serve an important role in Australia's domestic heating sector. They provide a cheap heating option for many families; particularly those not connected to natural gas. They use a renewable fuel source (provided firewood supplies are properly managed) that does not add to a net greenhouse gas release. Woodsmoke is a critical issue for the industry and cleaner burning appliances will need to be developed. Even with current technology, it should be possible to reduce wood-smoke to one fifth current levels within ten years in Australia, without reducing the number of homes using firewood. At present a constructive and cooperative approach to solving the problem has been adopted by the industry and pollution control authorities. A failure to achieve reductions in woodsmoke within a few years may see legislative pressure to restrict firewood use in urban areas.
The Australian industry has the potential to develop significant export capacity of clean burning, efficient heating and cooking appliances. International pressures to reduce greenhouse gas emissions suggest that firewood may have a bright future. If sustainably managed, firewood recycles carbon from the atmosphere. Firewood plantations can also serve other ecologically desirable functions such as wastewater treatment, salination reduction, erosion control, wildlife habitat and aesthetics. It is more energy efficient to use the firewood in the home than fuel an electric power station with biomass and then use the electricity to heat the home.

Further Information

RISE Resources - Information regarding available renewable energy resources.

RISE Technologies - An extensive collection of information regarding renewable energy technologies.

RISE Applications & System Design - Renewable energy application information and system designs.

RISE System Displays - Case studies and information on installed renewable energy systems & performance data.

An excellent resource is the Wood-Smoke handbook: woodheaters, firewood and operator practice written by Dr John Todd in 2003. This handbook includes such topics as combustion, woodheater design, emissions, heath and environmental impacts, Australian standards, wood types and alternative heating.

Shelton JW, 1983; Solid Fuels Encyclopedia; Garden Way Publishing, Charlotte, Vermont USA.
This is the most comprehensive book available on firewood and woodheaters. It is written for an American audience and is now out of date as far as the latest designs of woodheater are concerned. But it provides accurate and detailed information about all aspects of wood heating.

This is the Australian Home Heating Association site. It contains background information on the Australian woodheater industry, a discussion of wood-smoke pollution and generally promotes the use of woodheaters. This privately maintained site provides very useful information about woodheaters and has useful links to other sites.

An informative on-line book about wood-burning prepared by Natural Resources, Canada

These two sites provide a scathing attack on woodheaters and wood-smoke. They cover a good range of valuable literature, but are highly selective in the quotes they choose to support their case.

References

DEH (Department of the Environment and Heritage), 2004 "National Woodheater Audit Programme Report" (Online) http://www.deh.gov.au/atmosphere/airquality/publications/pubs/audit-program.pdf (Accessed 21 February 2007).

Driscoll, D., Milkovits, G., Freudenberger, D., 2000. “Impact and Use of Firewood in Australia” (Online) http://www.environment.gov.au/land/publications/firewood-impacts/firewood2.html (Accessed 20 February 2007).

Environmental Protection and Heritage Council, 2006. (Online) http://www.ephc.gov.au/ (Accessed 21 February 2007).

Todd, JJ., 2004; Health Impacts of Woodsmoke in Tasmania, In-House Fuelwood Report 66, Eco-Energy Options Pty Ltd, Hobart Australia.

Swartz, J., 1993. "Air Pollution and Daily Mortality in Birmingham, Alabama" (Online) http://aje.oxfordjournals.org/cgi/reprint/137/10/1136 (Accessed 21 February 2007).

Vedal, S., 1997; Ambient particles and health: lines that divide, Journal of the Air and Waste Management Association 47, 551-581 (Online) http://scholar.google.com/scholar?hl=en&lr=&q=cache:3-iZuq_bZs0J:www.awma.org/journal/pdfs/1997/5/vedal.pdf. (Accessed 20 February 2007).

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