The chapter on sizing and selection of HVAC equipment and components using rules of thumb provides a practical approach to designing efficient HVAC systems. It highlights simplified guidelines and rules of thumbs that assist engineers and technicians in estimating the size and capacity of equipment like cooling and heating coils, dampers, silencers, filters, expansion and buffer tanks, valves, pumps and fans. Emphasizing the importance of balancing efficiency, and performance, the chapter explains key factors to size and select various HVAC components. While rules of thumb are valuable for quick estimates and preliminary designs, the chapter underscores the importance of verifying these estimates with detailed calculations or software modelling for accuracy and compliance with industry standards.