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1 Introduction

The Warm Homes project was set up by the Ministry for the Environment to look at ways to encourage New Zealand households to move to cleaner heating sources and increase household energy efficiency, and overall to encourage warmer and healthier homes.

The aim of this study was to gain a better understanding of emission factors1 for wood-pellet burners. Wood-pellet burners were chosen because there is very little data on their real-life emissions. These burners are an emerging technology in New Zealand and their numbers are expected to grow, which will make it increasingly important to have an understanding of their emissions and how these may affect an air shed.

Of the four wood-pellet burners tested, one was found to be faulty. The average emission from the faulty burner was 11.35 g/kg, which was much higher than the other three burners and brought the average emissions from the four burners to 3.9 g/kg. Excluding the emissions from the faulty burner the average emission was 1.4 g/kg.

The Ministry recommends that the emission factors for pellet burners calculated in this report be applied in air shed modelling because they represent the best available information on real-life emissions in New Zealand. In doing so, users will need to assume a percentage of faulty burners to realistically approximate real-life emissions. However, as with all emission factors based on limited data, we advise caution. It is important to take into account the small sample size, test methodology, faulty burners and narrow range of burner designs covered.

1 'Emission factor' refers to a unit of particulate matter (PM10) discharged for every unit of fuel consumed. The emission factors in this report are expressed in grams of particulate per kilogram of fuel burnt where the weight of fuel is expressed on a dry weight basis.