This guide contains the necessary information that you may need when working as a heating engineer. For convenience, everything is systematized: basically, only formulas, diagrams and data are collected in tables. All data is either documented (the source of the data is indicated) or from personal experience (this data can be treated with skepticism, since this is only personal experience). Everything is written in simple language, since this is not a scientific publication, but a work assistant. Since this guide is constantly being revised and expanded, feedback is welcome.