This study discusses the heat exchange optimization of a 450kW water heater that runs on natural gas and in cofiring mode burning solid pulverized rumen and NG. The rumen material is a byproduct from cattle slaughter processes, consisting of the waste contained in the cow stomachs and intestines. The paper presents experimental analysis on a scaled prototype of 45kW and the results are complemented with CFD analysis of the aerothermochemistry of the combustion chamber and heat exchanger. In natural gas mode, the gaseous fuel provides 100% of the heat input, and in cofiring mode 50% of the heat rate input is obtained from the rumen contents and NG balances the heat rate. The combustion reaction is stabilized using a low swirl injector and a conic quarl. The optimization of the design seeks to use swirling flows inside the combustion chamber to improve convective heat transfer from the combustion products to the water-cooled surfaces, and the use of decaying swirl generator devices to enhance heat transfer during the second and third passes of the gases in the exchanger. The geometry variations attain effectiveness above 86%, with low emissions CO, THC, other pollutants, and to attain reaction stability of the rumen biowastes.