at the point where the volatile gases and or particulate material pass from the primary combustion zone 4 to the secondary combustion zone 5 one of the reasons for the popularity of air controlled wood burners is that the rate of combustion can be controlled through control of the air intake or oxygen however starving the fire of air results usually results in incomplete combustion and increased pollution the combustion system 1 uses oxygen liberated from steam to help the combustion process thereby making it less polluting to restrict the air flow into the wood burner 2 having regard to fig3 there is shown a cut away side perspective view of another possible embodiment of the present invention for convenience the same numbers are used in fig3 that correspond to the same or similar features which are also present in the embodiment described in fig1 and 2 fig3 illustrates an alternative embodiment whereby the second air supply means includes an air channel 19 which penetrates the outside of the exhaust flue 7 and extends downwards into the secondary combustion zone 5 this is achieved by creating an aperture 20 in the side of the exhaust flue 7 at a point just above the firebox 8 of the wood burner 2 the air channel 19 may then be inserted through this aperture 20 and extended downwards into or adjacent the secondary combustion zone 5 at the bottom of the lower flue 11 the air travelling through this channel 19 is super heated by the exhausting flue gases within the lower exhaust flue 11 and the channel 19 therefore serves essentially.