All modern appliances are designed to operate with the doors shut (except when refuelling), allowing their specific air supply paths to work correctly. Stoves are only efficient when burning hot, and this is achieved by using the right combination of air supply for the conditions. Primary air feeds in at the base and is useful to start a fire, but is then best closed down entirely with Wood burners, and partially if burning coals. Secondary air is fed through unseen channels, superheated as it rises, and then exits into the stove at a higher level and burns fuel particles that would otherwise have escaped unburnt up the flue. Airwash or Tertiary air is similar but feeds in above the door, sending hot air around the glass, again burning fuel that would otherwise deposit on the glass. The relative positioning of the controls is not set in stone – only practice with the individual stove will determine the ideal settings.
Freestanding stoves may benefit from having a thermometer attached to the stovepipe, which will show the ideal average heat and offer guidance as when best to refuel.
The critical element of any appliance’s clean and efficient combustion is the flue system. This is outside the control of the appliance manufacturer. Having brought air into the stove efficiently, the products of combustion must then be removed efficiently and it is the flow of air (oxygen) through the fire and up the flue which creates the perfect combustion process. It is the role of the installer to assess or design a suitable flue system.