In 1959 were launched in the market vertical Cochran series II boilers with thermal efficiencies and a great production of steam for its size. His operation could be fully automatic, both operating with liquid fuels as solids. The improvement in materials and manufacturing processes resulted in more tubes could be installed in each unit, thus resulting the trellis package boiler. These boilers are classified according to the number of steps; that is, according to the number of times that the hot products of combustion pass through the boiler. The most common design corresponds to the boilers of three steps, being the first one combustion chamber and the following two steps through the tubes. Years later arise the boilers of reverse flame where the combustion chamber is shaped like a thimble; the burner is installed at its end normally open below the Center. The flame back on itself within the combustion chamber to return toward the front of the boiler. Smoke tubes surround the thimble and allow the passage of hot products of combustion to the rear part of the boiler and the chimney.
By the end of the twentieth century different engineers begin to develop the biomass boilers that comply with a number of technical principles that lead to a complete combustion with low emissions, high efficiency and used as fuel biomass, i.e. residues of organic matter that are renewable fuels, such as: Pellet, bones shells of walnuts and almonds, olivesremains of prunings, firewood is dry trees, etc. In these times the biomass boilers are the most used in all domestic and industrial areas because they have the advantages of using more economic and generous with environmentally friendly fuels.