We have developed high temperature gas sensors for flue gases from various combustions. With signals from CO and O2 concentrations in the flue gas we can optimize the combustion with the airflow with a feedback system. The efficiency of the combustion improves, less sot and less bad smell from hydrocarbons. This way more biofuel can be used in a better way in households than what is done today. Our sensors is also developed for NOX and NH3 so with more biofuel mixed in diesel much transportation ( for trucks and ships) can be used for another many decades. Both these applications is an easy way to replace fossil fuel with biofuel for Net Zero CO2 emission.