A typical Australian wood heater emits about 10 grams of PM2.5 per hour, and is often used on cold days and nights when temperature inversions trap the air close to the ground.  In 2 hours, a source emitting 10 grams per hour is enough to generate PM2.5 concentrations of 50 ug/m3 over an area area 200 metres x 200 metres to a height of 10 metres.  This suggests that it would be unwise to live within 200 metres of a house using a slow combustion wood heater as the main source of heating, especially if the prevailing wind blows the pollution in your direction. For anyone who cares about health deals: http://paylesswithcoupons.com/