How wood-burning stove combustion systems work

A modern wood-burning stove usually has three independent air systems. These air systems feed oxygen to the burning firewood. These systems may vary from stove to stove, but are usually as described here:

Primary air

Primary air is characterised as the air that enters beneath the fire in the stove. Primary air is only used during kindling and, in some cases, when reigniting. During kindling, the fire should be burning well with high flames, as the stove and chimney should be warm before shutting the primary air off. When reigniting, close off the primary air when the fire has taken proper hold, typically when the wood has charred black.

Secondary air

The secondary air is also known as air wash. Air enters at the top of the stove and will be directed down the front pane and then into the fire. These air currents are what prevent soot from forming on the glass panes.

Secondary air is used to control the combustion. Never reduce secondary air flow so far that the flames stop being clear and vibrant.

Tertiary air

Tertiary air is used to burn off the hot gas and particles as they evaporate from the wood and are not burnt in the actual fire. Air quantity is carefully configured in the wood-burning stove and cannot usually be adjusted.

VARDE STOVES – Airflow adjustment on a VARDE stove from Varde Ovne on Vimeo.

External air – VARDE AirBox

Modern buildings are often very dense, which can make it difficult to bring in enough air for the purpose of combustion. Some VARDE stoves are equipped with our AirBox system, which can suck air in from the outside. This requires the routing of a hose to outside the house, typically through an external wall. This produces improved combustion, ensuring a proper, healthy indoor climate in your home.

 It is important, however, that you fire your wood-burning stove correctly, to ensure that the air in the room does not become too dry.

Take a look here to see how to fire your wood-burning stove correctly


All VARDE wood-burning stoves are convection stoves. A convection stove works by sucking cold air into the base of the stove. Air is fed between the walls of the combustion chamber and the outer panels of the stove. When the warm air reaches the top of the stove, it is blown out and diffused into the room.

The advantage of a convection stove is that the resulting air circulation produces a comfortable form of heating, as the air is better distributed into the room.

Many older wood-burning stoves are not convection stoves. Because these radiation stoves do not have channels for natural air circulation heated by the combustion chamber, the heat they they produce is concentrated in a small area around the stove and does not provide heat further away from the stove.

Safety distances for a radiation stove will typically be larger than for convection stoves. This means having to take care not to position furniture and other household items too close to the stove because of the intense heat close to the stove.

Distribute the heat into the room

No matter whether your wood-burning stove produces convection heat or radiates heat, you can distribute the heat further away from the stove into the room. Putting a fan on top of the stove allows the heat to be blown further out into the room.

See our range of fans here.