Fires smoke and pollute it they do not burn intensely. A temperature of 300 – 350 degrees Celsius is required to burn all the gases emmited from wood. At a lower temperature, the gases (smoke) will go up the chimney unburned. For this reason, a hot fire will burn cleanest; all the pollution is simply turned into heat. You will get a good indication of how efficiently your fire is operating, by simply going outside to check the colour of the smoke. There should only be a thin, pale emission from the chimney. Once your house is warm, control the temperature by the amount of wood you add not by closing the airvent.