fuels are illustrated in fig1 6 fig1 shows a rectangular shaped combustion cage 10 for wood pellet or other solid biomass fuel having a front wall 20 a back wall 20 39 a first side wall 22 and a second side wall 22 39 connected end to end to each other at side wall seams 23 and to a bottom 24 forming a box front wall 20 back wall 20 39 side walls 22 and 22 39 and bottom 24 define a combustion space 26 for receiving wood pellet and other solid biomass fuel front and back walls 20 and 20 39 respectively side walls 22 and 22 39 and bottom 24 each contain a plurality of holes 28 which allow combustion air to penetrate the fuel mass contained within combustion space 26 even though a hole to solid surface ratio of less than 40 renders combustion cage 10 operational a hole to solid surface ratio of at least 40 is preferred for efficient operation of the present invention the plurality of holes 28 are preferably evenly spaced from each other perforated sheet metal wire mesh wire cloth or other suitable material having the necessary hole to solid surface ratio may be used fig7 shows an enlarged view of the typical wire mesh wire cloth 70 and perforations 28 of the preferred material it.