Wood is Good
The Australian Greenhouse Office has stated “… in terms of limiting net greenhouse gas emissions, firewood is generally more favourable for domestic heating than other sources of domestic heating such as gas and electricity” (page 6). This was based on a study undertaken by the CSIRO. CSIRO also found that there was actually a positive net sequestration of carbon per unit of energy produced from burning firewood harvested from plantations (page 6).
Site-built masonry appliances are specifically excluded from AS/NZS 4013 as they are site built; each one differs. This contrasts a commercially available ‘metal box’ type heater where they are all the same.
Research in USA shows shows that emissions for masonry heaters range from 0.5 – 2.0 g/kg. This is less that the limit set in the Australian Standard (4g/kg).
We contacted a laboratory in Australia accredited to test to AS/NZS 4013 to see if we could have them test our heater. They said that this was not possible. We are still looking for someone to test it.
The life cycle assessment of greenhouse gas emissions from domestic wood heating conducted by the Department of Environment and Heritage in 2003 showed that greenhouse gas emissions are lower for wood heating than they are for electricity or gas. They concluded that in regard to the minimising of greenhouse gas emissions “firewood is generally more favourable for domestic heating than other sources of domestic heating such as gas and electricity” http://utting.net.au/doc/lifecycle.pdf. This can be seen in the following graph.
Because this graph shows figures for ‘standard wood heaters’ used in Australia, the greenhouse gas emissions from a masonry heater are even lower than those shown.
The Australian Standards do not specify an efficiency level. In 2006, the Department of the Environment and Heritage stated that no jurisdiction in Australia required wood heaters to meet a minimum efficiency level. While many jurisdictions are considering introducing minimum efficiency criteria of 60 – 65% we haven’t been able to identify any that have yet.
At the moment, the average operational efficiency for wood heaters in Australia is 61%. Masonry heaters typically attain operational efficiencies of 80%. Independent laboratory testing of the Tempcast heater in North America demonstrated an operational efficiency of 80% and combustion efficiency of almost 95%. There are no other wood heaters in Australia that reach this level of efficiency.
How to minimise emissions and maximise efficiency
The way you operate your heater will impact the emissions and efficiency. The key things to do are:
- Burn the fire hot and fast. The faster you can get the fire going the less smoke there will be.
- Use dry timber and do not burn green wood. The higher the moisture content, the more emissions will be produced and the lower the efficiency.
- Build your fire as a ‘top down’ fire – the big wood at the bottom and the kindling at the top. This increases the efficiency of the burn.
For in-depth reading on timber burning and emissions click on these links to Australian research publications: