The primary air is drawn into the stove through the slide on the door. The secondary air is regulated with the aid of a slider above the door. The heated secondary air flows down the viewing window and then feeds the fire; it is this secondary combustion that completes the burning cycle by turning unburned volatiles into flame.
As much as half of the heat obtainable from wood is obtained from this secondary combustion. It is important that the firebox temperature is maintained at a high level as this also aids complete combustion. The use of a stove pipe thermometer is recommended, as this will indicate stove performance. For Example, when first lighting a stove it is important to get it really hot before closing the burning rate down. The firebox temperature should reach 400C which equates to approximately 250C at the flue pipe.
If the stove is operated at this optimum level very clean combustion can be achieved with little or no smoke visible from the chimney.