The title of this publication is quite self-explanatory. The book is mainly focusing on the matetr of thermal design and some important performance aspects of the fire-tube and water-tube waste heat boilers, steam generators and other relevant equipment including economizers and air heaters. The author of the book has worked out more than a hundred of real-life practical issues presenting them in a way that would be helpful for the boiler plant engineer to evaluate the newly installed boiler plants or make modification to the existing boiler arrangements without having to approach the boiler manufacturers or suppliers for assistance. All key technological trends and developments relating to the design and construction of the boilers have been covered in this volume in order to prevent the new ideas for the improvement of the efficiency of the boilers and also with the intention to lower the drop in gas pressure. The book will also help practicing boiler plant engineers to better understand and correctly evaluate the performance of the steam generator/waste heat boilers they maintain. Numerous very informative calculation procedures have also been included in this book; in addition, the appendices to the main body of the book contain the simplified procedures of estimation of the heat transfer coefficients.