Stoves described as clean burning wood stoves are very efficient in the way it burns wood. The actual wood burning occurs because of gases contained inside the fuel. It is this gas that actually does the burning. As with any type of burning, combustion of this gas requires a supply of oxygen which is normally taken from the air. The trouble is, this can get used up quickly. This is the beauty of something called ‘secondary combustion’. When a new oxygen supply is introduced via air inlets which draw air to the top of the firebox, gases which normally go straight up the flue are also burnt.
This has two big advantages. Firstly, with clean burning wood stoves there is more heat created. And second, it reduces harmful emissions. Some stoves which are clean-burning receive official approval in smoke-free zones purely because of these lower emissions.
Because clean burning stoves generate more heat through gases which would have been wasted, they do have a higher output than standard wood burning stoves and they also use less fuel. Another pleasing side-effect is that the user will see more vivid flames, as gases are seen to combust in the air above the fuel.
The more highly efficient the stove, the cleaner burning it can be said to be. A greater amount of the particulates from wood are burnt, so the wood delivers much more in terms of heat and therefore efficiency. this in turn means less pollutants to escape via the chimney. If a stove is said to be almost 85% efficient it will be because it is cleaner than a wood burning stove with an efficiency of 70%. And remember, just because a stove is said to have a higher output, that does not mean it is a clean burning wood stove. It might just have more capacity for fuel.