This study has increased our understanding of emissions factors for NES-compliant wood burners, which is important for air quality practitioners responsible for calculating emission inventories. The average real-life emission for the nine NES-compliant wood burners was found to be 4.6 g/kg. The 95% confidence interval around this mean is 2.6 6.6 g/kg (note that the mean is the midpoint of the confidence interval).
It is premature to conclude that emission factors from NES-compliant wood burners are lower by an order of magnitude compared to old wood burners. Nevertheless, these results are reassuring because they indicate that emission factors from NES-compliant wood burners are lower than for pre-1994 wood burners. This is especially reassuring when compared to the results from Scott (2005).
These results support Ministry policy and show that the NES design standard is an effective tool for reducing emissions. The relationship between moisture and emissions from this test is clear – wet wood does not burn as cleanly as dry wood. However, this does not mean that dry wood is better all of the time.
The Ministry recommends that the emission factors calculated in this report be applied in air shed modelling because this represents the best available information on real-life emissions in New Zealand. However, as with all emission factors based on limited data, we advise exercising caution. It is important to take into account the small sample size, test methodology and narrow range of burner designs covered.